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At least 379 records · Page 21Linked to original sources
PubMed1999

The Na(+)-F(1)F(0)-ATPase operon from Acetobacterium woodii. Operon structure and presence of multiple copies of atpE which encode proteolipids of 8- and 18-kda.

Eight genes (atpI, atpB, atpE(1), atpE(2), atpE(3), atpF, atpH, and atpA) upstream of and contiguous with the previously described genes atpG, atpD, and atpC were cloned from chromosomal DNA of Acetobacterium woodii. Northern blot analysis revealed that the eleven atp genes are transcribed as a polycistronic message. The atp operon encodes the Na(+)-F(1)F(0)-ATPase of A. woodii, as evident from a comparison of the biochemically derived N termini of the subunits with the amino acid sequences deduced from the DNA sequences. The molecular analysis revealed that all of the F(1)F(0)-encoding genes from Escherichia coli have homologs in the Na(+)-F(1)F(0)-ATPase operon from A. woodii, despite the fact that only six subunits were found in previous preparations of the enzyme from A. woodii. These results unequivocally prove that the Na(+)-ATPase from A. woodii is an enzyme of the F(1)F(0) class. Most interestingly, the gene encoding the proteolipid underwent quadruplication. Two gene copies (atpE(2) and atpE(3)) encode identical 8-kDa proteolipids. Two additional gene copies were fused to form the atpE(1) gene. Heterologous expression experiments as well as immunolabeling studies with native membranes revealed that atpE(1) encodes a duplicated 18-kDa proteolipid. This is the first demonstration of multiplication and fusion of proteolipid-encoding genes in F(1)F(0)-ATPase operons. Furthermore, AtpE(1) is the first duplicated proteolipid ever found to be encoded by an F(1)F(0)-ATPase operon.

Amino Acid Sequence↗
PubMed2001

Identification and structural characterization of nucleus-encoded transfer RNAs imported into wheat mitochondria.

Despite its large size (200-2400 kilobase pairs), the mitochondrial genome of angiosperms does not encode the minimal set of tRNAs required to support mitochondrial protein synthesis. Here we report the identification of cytosolic-like tRNAs in wheat mitochondria using a method involving quantitative hybridization to distinguish among three tRNA classes: (i) those encoded by mitochondrial DNA (mtDNA) and localized in mitochondria, (ii) those encoded by nuclear DNA and located in the cytosol, and (iii) those encoded by nuclear DNA and found in both the cytosol and mitochondria. The latter class comprises tRNA species that are considered to be imported into mitochondria to compensate for the deficiency of mtDNA-encoded tRNAs. In a comprehensive survey of the wheat mitochondrial tRNA population, we identified 14 such imported tRNAs, the structural characterization of which is presented here. These imported tRNAs complement 16 mtDNA-encoded tRNAs, for a total of at least 30 distinct tRNA species in wheat mitochondria. Considering differences in the set of mtDNA-encoded and imported tRNAs in the mitochondria of various land plants, the import system must be able to adapt relatively rapidly over evolutionary time with regard to the particular cytosolic-like tRNAs that are brought into mitochondria.

Base Sequence↗
PubMed2002

The functional locus of intrusions: encoding or retrieval?

Many current accounts of the origin of intrusions and other confabulatory-like phenomena emphasize the role of a retrieval or postretrieval deficit in these disorders. In the experiments reported herein we examine whether the presence of an interfering task at encoding elicits more intrusions in normal subjects than the presence of an interfering task at retrieval. In Experiment 1, performance in story recall without interference was compared to the performance with an interfering task at retrieval. In Experiment 2, the performance in story recall with an interfering task at encoding was compared to performance in story recall with interference at encoding and retrieval. Results suggest that interference at retrieval has no effect on the accuracy of recall and on intrusions. Interference at encoding compared to interference at encoding and retrieval (Experiment 2) had no effect on the accuracy of recall and on frequency of intrusions. Cross-experiment comparisons suggest that interference at encoding affects both the accuracy of retrieval and the probability of intrusions in recall. These results suggest that encoding processes, more than retrieval processes, have a role in eliciting intrusions.

Adult↗
PubMed2001

Material-specific lateralization in the medial temporal lobe and prefrontal cortex during memory encoding.

Numerous observations in patients with unilateral lesions of the medial temporal lobe (MTL) and the prefrontal cortex indicate that memory processes are lateralized according to content. Left-sided lesions interfere with verbal memory processes, whereas right-sided lesions interfere with visuospatial (non-verbal) memory processes. However, functional imaging studies have resulted in contradictory data, some studies showing lateralization in the prefrontal cortex determined by stage of processing (encoding versus retrieval) and others suggesting that lateralization is dependent on the type of material. Few studies have examined this issue in the MTL. In order to test the hypothesis that the lateralization of encoding processes in the MTL and frontal regions is dependent on the verbalizability of the material, we performed behavioural and functional imaging studies. We demonstrated differing verbalizabilities of three classes of non-verbal stimuli (scenes > faces > abstract patterns) using a dual-task verbal interference behavioural paradigm. A functional neuroimaging study of encoding was carried out using these three types of stimuli, plus words. During whole-brain functional MRI at 1.5 T, eight normal right-handed adults were presented with alternating blocks of novel and repeated stimuli under intentional memory encoding conditions. Verbal encoding resulted in left-lateralized activation of the inferior prefrontal cortex and the MTL. Pattern encoding activated the right inferior prefrontal cortex and the right MTL. Scenes and faces resulted in approximately symmetrical activation in both regions. The data indicate that the lateralization of encoding processes is determined by the verbalizability of stimuli.

Adolescent↗
PubMed2004

Prefrontal cortex asymmetry for memory encoding of words and abstract shapes.

Previous work suggested a differential contribution of prefrontal cortex (PFC) to successful encoding depending on the stimulus material. Here, we tested the hypothesis that encoding of words preferentially involves the left PFC, while encoding of nonverbal items (abstract shapes) relies on the right PFC. We used an experimental design that evaluated encoding of both words and abstract shapes in the same healthy volunteers. A transient virtual lesion of the left or the right PFC was elicited with transcranial magnetic stimulation (TMS) while subjects memorized verbal and nonverbal items. We found that encoding of verbal material was disrupted by left PFC stimulation, whereas encoding of nonverbal material was disrupted by right PFC stimulation. These results demonstrate a functionally relevant lateralization of prefrontal contribution for verbal and nonverbal memory encoding.

Adult↗
PubMed2004

Ketamine disrupts frontal and hippocampal contribution to encoding and retrieval of episodic memory: an fMRI study.

The N-methyl-D-aspartate (NMDA) receptor antagonist ketamine produces episodic memory deficits. We used functional magnetic resonance imaging to characterize the effects of ketamine on frontal and hippocampal responses to memory encoding and retrieval in healthy volunteers using a double-blind, placebo-controlled, randomized, within-subjects comparison of two doses of intravenous ketamine. Dissociation of the effects of ketamine on encoding and retrieval processes was achieved using two study-test cycles: in the first, items were encoded prior to drug infusion and retrieval tested, during scanning, on drug; in the second, encoding was scanned on drug, and retrieval tested once ketamine plasma levels had declined. We additionally determined the interaction of ketamine with the depth of processing that occurred at encoding. A number of effects upon task-dependent activations were seen. Overall, our results suggest that left frontal activation is augmented by ketamine when elaborative semantic processing is required at encoding. In addition, successful encoding on ketamine is supplemented by additional non-verbal processing that is incidental to task demands. The effects of ketamine at retrieval are consistent with impaired access to accompanying contextual features of studied items. Our findings show that, even when overt behaviour is unimpaired, ketamine has an impact upon the recruitment of key regions in episodic memory task performance.

Adolescent↗
PubMed1999

Cloning and expression of a human gene encoding an N-acetylgalactosamine-alpha2,6-sialyltransferase (ST6GalNAc I): a candidate for synthesis of cancer-associated sialyl-Tn antigens.

The sialyl-Tn (sTn) antigen is a well known cancer-associated antigen, the expression of which is related to the prognosis of cancer patients. We aimed to isolate a human gene encoding an N -acetylgalactosamine alpha2,6-sialyltransferase which synthesizes sTn antigen, and to characterize the enzyme. Degenerate primers encoding sialyl motifs were used for the polymerase chain reaction to amplify complementary DNAs prepared from RNAs of human pyloric mucosae with intestinal metaplasia, which abundantly expressed sTn antigen, followed by screening of full-length cDNAs using the amplified DNA fragment as a probe. We isolated two human cDNA clones, long-form (2.46 kb) and short-form (2.23 kb) cDNAs. The former encodes an active enzyme with a predicted 600 amino acid sequence. The latter, a splice-variant of the long-form, encodes an inactive enzyme. HCT15 human colorectal cancer cells stably expressing the long-form cDNA expressed sTn epitopes on O -glycans. The long form cDNA was considered to encode a human homologue of chick ST6GalNAc I for the following reasons: (1) the putative amino acid sequence showed greater homology to that of chick ST6GalNAc I (55%) compared to other sialyltransferases, (2) it encodes the extraordinarily long stem region that is a typical feature of chick ST6GalNAc I, and (3) the substrate specificity was very similar to that of chick ST6GalNAc I. In situ hybridization demonstrated that the localization of transcripts correlated well with that of sTn antigen in gastric cancer cells and Goblet cells in intestinal metaplastic glands. Thus, we determined that the long-form cDNA of the human ST6GalNAc I gene encodes the probable candidate for the human sTn synthase(s).

Acetylglucosamine↗
PubMed2003

Factors influencing gene expression and resistance for Gram-negative organisms expressing plasmid-encoded ampC genes of Enterobacter origin.

High-level expression of AmpC beta-lactamases results in organisms resistant to multiple beta-lactam antibiotics. The mechanism of chromosomally mediated AmpC resistance has been elucidated, however the mechanism(s) driving plasmid-encoded AmpC resistance are unknown. Studies were designed to identify factors which influence expression of plasmid-encoded ampC genes and correlate these factors with resistance. As the model system, ampC genes of Enterobacter origin were used to determine how gene copy number, genetic background and genetic organization influenced resistance phenotypes. To this end, gene expression from the plasmid-encoded inducible blaACT-1 and non-inducible blaMIR-1 were compared with chromosomal ampC gene expression from both wild-type (WT) and derepressed Enterobacter cloacae isolates. RNA levels within the original clinical isolates were examined using primer extension analysis, whereas a new PCR strategy was developed to examine gene copy number. These data revealed that blaACT-1 and blaMIR-1 constitutive expression was 33- and 95-fold higher than WT expression, whereas copy numbers of the plasmid-encoded genes were 2 and 12, respectively. Differences in promoters and transcriptional starts for the respective plasmid-encoded genes were noted and contribute to increases observed in overall expression. Finally, beta-lactam MICs were increased two- to 16-fold when blaACT-1 was expressed in Escherichia coli AmpD- strains compared with E. coli AmpD+ strains. In conclusion, high-level expression of plasmid-encoded ampC genes requires interplay between multiple factors including genetic organization, promoter modifications, genetic background, and to some extent gene copy number. In addition, clinical laboratories need to be aware that genetic backgrounds of inducible plasmid-encoded genes can dramatically influence MICs for organisms not normally associated with derepressed phenotypes.

Anti-Bacterial Agents↗
PubMed1990

De novo purine nucleotide biosynthesis: cloning of human and avian cDNAs encoding the trifunctional glycinamide ribonucleotide synthetase-aminoimidazole ribonucleotide synthetase-glycinamide ribonucleotide transformylase by functional complementation in E. coli.

The trifunctional enzyme encoding glycinamide ribonucleotide synthetase (GARS)-aminoimidazole ribonucleotide synthetase (AIRS)-glycinamide ribonucleotide transformylase (GART) was cloned by functional complementation of an E. coli mutant using an avian liver cDNA expression library. In E. coli, genes encoding these separate activities (purD, purM, and purN, respectively) produce three proteins. The avian cDNA, in contrast, encodes a single polypeptide with all three enzyme activities. Using the avian DNA as a probe, a cDNA encoding the complete coding sequence of the trifunctional human enzyme was also isolated and sequenced. The deduced amino acid sequence of the human and avian polyproteins show extensive sequence homologies to the bacterial purD, purM, and purN encoded proteins. Avian and human liver RNAs appear to encode both a trifunctional enzyme (G-ARS-AIRS-GART) as well as an RNA which encodes only GARS. The trifunctional protein has been implicated in the pathology of Downs Syndrome and molecular tools are now available to explore this hypothesis. Initial efforts to compare the expression of GARS-AIRS-GART between a normal fibroblast cell line and a Downs Syndrome cell line indicate that the levels of RNA are similar.

Acyltransferases↗
PubMed1996

Regulation of steady-state concentrations of messenger ribonucleic acid encoding prostaglandin F2 alpha receptor in ovine corpus luteum.

To investigate the regulation of ovine luteal receptors for prostaglandin F2 alpha (PGF2 alpha), reverse transcription-polymerase chain reaction was used to produce a 284-bp partial cDNA that was 98% identical to that reported for the bovine PGF2 alpha receptor (PGF2 alpha-R). In situ hybridization localized mRNA for PGF2 alpha-R specifically to large luteal cells. In experiment 1, pools of luteal tissue (n = 4/day) collected from ewes on Days 3, 6, 9, 12, and 15 of the estrous cycle were analyzed for mRNA encoding PGF2 alpha-R. There was no difference in mean steady-state concentrations of mRNA encoding PGF2 alpha-R among any of the days studied (range = 2.3 +/- 0.3 to 3.5 +/- 0.7 fmol PGF2 alpha-R mRNA/ microgram poly[A]+ RNA as assessed by slot-blot hybridization). In experiment 2, ewes on Day 11 or Day 12 of the estrous cycle were administered PGF2 alpha, and corpora lutea were collected 4, 12, or 24 h later (n = 4-5 per time point). Nontreated (n = 4) or saline-treated (n = 4) ewes served as controls. Luteal concentrations of mRNA encoding PGF2 alpha-R were decreased (p < 0.05) at 4, 12, and 24 h after injection of PGF2 alpha. In experiment 3, ewes (midluteal phase) were administered saline, PGF2 alpha, phorbol 12-myristate 13-acetate (PMA), or LH via ovarian arterial injection, and luteal tissue was collected 0, 4, 12, or 24 h later (n = 3-4 per treatment per time). Steady-state concentrations of mRNA encoding PGF2 alpha-R were decreased (p < 0.05) by PGF2 alpha and PMA treatment (4 and 12 h) but were increased (p < 0.05) at 24 h after LH treatment. In summary, 1) mRNA encoding PGF2 alpha-R was localized to large luteal cells; 2) concentrations of mRNA encoding PGF2 alpha-R did not vary during the estrous cycle; 3) treatment with PGF2 alpha or PMA to activate protein kinase C decreased concentrations of PGF2 alpha-R mRNA within 4 h of treatment; and 4) administration LH increased concentrations of mRNA encoding PGF2 alpha-R 24 h following injection.

Animals↗
PubMedDate not supplied

Neural activity during encoding predicts false memories created by misinformation.

False memories are often demonstrated using the misinformation paradigm, in which a person's recollection of a witnessed event is altered after exposure to misinformation about the event. The neural basis of this phenomenon, however, remains unknown. We used fMRI to investigate encoding processes during the viewing of an event and misinformation to see whether neural activity during either encoding phase could predict what would be remembered. fMRI data were collected as participants studied eight vignettes (Original Event phase). Shortly afterward, participants studied the same vignettes during scanning, but with changes to several details, serving as the misinformation (Misinformation phase). Two days later, their memories for the Original Event were assessed. Activity that subsequently led to true and false memories was examined during both encoding phases. Two interaction patterns between encoding phase (Original Event and Misinformation) and type of memory (true and false) were observed in MTL and PFC regions. In the left hippocampus tail and perirhinal cortex, a predictive item-encoding pattern was observed. During the Original Event phase, activity was greater for true than false memories, whereas during the Misinformation phase, activity was greater for false than true memories. In other regions, a pattern suggestive of source encoding was observed, in which activity for false memories was greater during the Original Event phase than the Misinformation phase. Together, these results suggest that encoding processes play a critical role in determining true and false memory outcome in misinformation paradigms.

Adolescent↗
PubMed2005

Proanthocyanidin synthesis and expression of genes encoding leucoanthocyanidin reductase and anthocyanidin reductase in developing grape berries and grapevine leaves.

Proanthocyanidins (PAs), also called condensed tannins, can protect plants against herbivores and are important quality components of many fruits. Two enzymes, leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR), can produce the flavan-3-ol monomers required for formation of PA polymers. We isolated and functionally characterized genes encoding both enzymes from grapevine (Vitis vinifera L. cv Shiraz). ANR was encoded by a single gene, but we found two highly related genes encoding LAR. We measured PA content and expression of genes encoding ANR, LAR, and leucoanthocyanidin dioxygenase in grape berries during development and in grapevine leaves, which accumulated PA throughout leaf expansion. Grape flowers had high levels of PA, and accumulation continued in skin and seeds from fruit set until the onset of ripening. VvANR was expressed throughout early flower and berry development, with expression increasing after fertilization. It was expressed in berry skin and seeds until the onset of ripening, and in expanding leaves. The genes encoding LAR were expressed in developing fruit, particularly in seeds, but had low expression in leaves. The two LAR genes had different patterns of expression in skin and seeds. During grape ripening, PA levels decreased in both skin and seeds, and expression of genes encoding ANR and LAR were no longer detected. The results indicate that PA accumulation occurs early in grape development and is completed when ripening starts. Both ANR and LAR contribute to PA synthesis in fruit, and the tissue and temporal-specific regulation of the genes encoding ANR and LAR determines PA accumulation and composition during grape berry development.

Base Sequence↗
PubMed1994

Isolation and characterization of cDNAs encoding the vacuolar H(+)-pyrophosphatase of Beta vulgaris.

The H(+)-pyrophosphatase (V-PPase) of plant vacuolar membranes catalyzes the electrogenic translocation of H+ from the cytosol to vacuole lumen and, in parallel with the vacuolar H(+)-ATPase located in the same membrane, establishes the inside-acid, inside-positive H(+)-electrochemical potential difference responsible for energizing the H(+)-coupled transport of solutes into the vacuole. The results of previous investigations suggest that the gene encoding the substrate-binding subunit of the V-PPase is present in a single copy in the genome of Arabidopsis thaliana (V. Sarafian, Y. Kim, R.J. Poole, P.A. Rea [1992] Proc Natl Acad Sci USA 89: 1775-1779), but it is not known whether the situation in Arabidopsis is typical of most vascular plants. With the objective of assessing the general applicability of this finding and acquiring sequence data for structure-function analyses of the enzyme from Beta vulgaris, we have sought to isolate cDNAs encoding the V-PPase from this organism by screening a Beta cDNA library constructed in lambda ZAP with the Arabidopsis cDNA insert (AVP) encoding the V-PPase. The results of these investigations demonstrate that at least two genes encode the V-PPase in Beta. Restriction and sequence analyses of the cDNAs from Beta reveal two classes, designated BVP1 and BVP2. BVP1 and BVP2 encode closely related but distinct polypeptides with computed masses of 80,550 and 80,000 D, respectively, exhibiting 88% identity with each other and 89% identity with the corresponding polypeptide from Arabidopsis. The nucleotide sequences of BVP1 and BVP2, on the other hand, are 70% identical within their coding regions but less than 28 and 53% identical within their respective 5' and 3' noncoding regions. Southern analyses of Beta genomic DNA confirm that two genes encode the V-PPase, and northern analyses of polyadenylated RNA isolated from a range of tissue types and probed with RNAs transcribed from the 3' noncoding sequences of BVP1 or BVP2 indicate that both genes are expressed in the intact plant. On the basis of these findings and the recent demonstration of then sufficiency of the substrate-binding polypeptide, alone, for all of the known catalytic functions of the V-PPase (E.J. Kim, R.-G. Zhen, P.A. Rea [1994] Proc Natl Acad Sci USA [91:6128-6132]), the two cDNA species isolated from Beta are concluded to encode variant, possibly isoforms, of the enzyme.

Amino Acid Sequence↗
PubMed2003

Genome-wide analysis of NBS-LRR-encoding genes in Arabidopsis.

The Arabidopsis genome contains approximately 200 genes that encode proteins with similarity to the nucleotide binding site and other domains characteristic of plant resistance proteins. Through a reiterative process of sequence analysis and reannotation, we identified 149 NBS-LRR-encoding genes in the Arabidopsis (ecotype Columbia) genomic sequence. Fifty-six of these genes were corrected from earlier annotations. At least 12 are predicted to be pseudogenes. As described previously, two distinct groups of sequences were identified: those that encoded an N-terminal domain with Toll/Interleukin-1 Receptor homology (TIR-NBS-LRR, or TNL), and those that encoded an N-terminal coiled-coil motif (CC-NBS-LRR, or CNL). The encoded proteins are distinct from the 58 predicted adapter proteins in the previously described TIR-X, TIR-NBS, and CC-NBS groups. Classification based on protein domains, intron positions, sequence conservation, and genome distribution defined four subgroups of CNL proteins, eight subgroups of TNL proteins, and a pair of divergent NL proteins that lack a defined N-terminal motif. CNL proteins generally were encoded in single exons, although two subclasses were identified that contained introns in unique positions. TNL proteins were encoded in modular exons, with conserved intron positions separating distinct protein domains. Conserved motifs were identified in the LRRs of both CNL and TNL proteins. In contrast to CNL proteins, TNL proteins contained large and variable C-terminal domains. The extant distribution and diversity of the NBS-LRR sequences has been generated by extensive duplication and ectopic rearrangements that involved segmental duplications as well as microscale events. The observed diversity of these NBS-LRR proteins indicates the variety of recognition molecules available in an individual genotype to detect diverse biotic challenges.

Amino Acid Sequence↗
PubMed1987

Structure and evolutionary origin of the gene encoding mouse NF-M, the middle-molecular-mass neurofilament protein.

We describe the complete sequence of the gene encoding mouse NF-M, the middle-molecular-mass neurofilament protein. The coding sequence is interrupted by two intervening sequences which align perfectly with the first two intervening sequences in the gene encoding NF-L (the low-molecular-mass neurofilament protein); there is no intron in the gene encoding NF-M corresponding to the third intron in NF-L. Therefore, both the number of introns and their arrangement in the genes coding NF-L and NF-M contrast sharply with the number and arrangement of introns in the genes of known sequence, encoding other members of the intermediate filament multigene family (desmin, vimentin, glial fibrillary acidic protein and the acidic and basic keratins); with the exception of a single truncated keratin gene that lacks an encoded tailpiece, these genes all contain eight introns, of which at least six are placed at homologous locations. Assuming the existence of a primordial intermediate filament gene containing most (if not all) the introns found in contemporary non-neurofilament intermediate filament genes, it seems likely that an RNA-mediated transposition event was involved in the generation of an ancestral gene encoding the NF polypeptides. A combination of insertional transposition and gene-duplication events could then explain the anomalous number and placement of introns within these genes. Consistent with this notion, we show that the genes encoding NF-M and NF-L are linked.

Amino Acid Sequence↗
PubMed1988

Prolonged noxious mechanical stimulation of the rat's tail: responses and encoding properties of dorsal horn neurones.

1. Single-unit electrical activity has been recorded from dorsal horn neurones in the sacral (S1-S2) segments of the spinal cord of barbiturate-anaesthetized rats. Fifty-two neurones responding to a manually applied pinch of their receptive fields in the tail were selected. They were subsequently tested for their responses to four successive 2 min pinches at noxious intensities delivered by a feed-back-controlled mechanical device. 2. Neurones were tested with both innocuous (i.e. brushing and stroking) and noxious (i.e. pinching, pin-prick, and in some cases heating about 45 degrees C) stimulation of their cutaneous receptive fields. Three of the tested cells were driven exclusively by innocuous skin stimulation (mechanoreceptive or class 1), thirty-six were driven by both innocuous and noxious skin stimulation (multireceptive or class 2) and thirteen were driven exclusively by noxious skin stimulation (nocireceptive or class 3). 3. All of the multireceptive and nocireceptive neurones responded to the 2 min noxious pinch with an initial phasic discharge followed by sustained firing that showed little evidence of adaptation throughout the stimulus period. The three mechanoreceptive neurones responded to the 2 min noxious pinch with a short discharge at the stimulus onset, but were silent for the remainder of the stimulus period. 4. Thirty-one cells were tested with successive 2 min pinches of 4, 6 and 8 N (and in some cases, a further 4 N pinch) applied at 10 min intervals. Different encoding properties were observed during the sustained part of the neuronal response according to: (i) the afferent fibre input characteristics of the cell; (ii) whether or not the tail had received a test series of pinches earlier in the same experiment. 5. None of the multireceptive cells with only an A-fibre afferent input encoded the stimulus strength. However, the multireceptive cells with both an A- and a C-fibre afferent input and all nocireceptive cells did encode the stimulus strength, providing that no previous noxious test stimuli had been applied to the tail. The encoding nocireceptive neurones had in general a steeper stimulus-response curve than the encoding multireceptive neurones, though the two groups overlapped to some extent. 6. Three encoding cells (two multireceptive and one nocireceptive) were tested with a second series of pinches (4, 6, 8 and 4 N), 40 min subsequent to the initial test series. These cells did not encode this second test series, but were more excitable, producing a greater response to a given test force.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1997

Pacemaker activity in a sensory ending with multiple encoding sites: the cat muscle spindle primary ending.

1. A combined physiological, histological and computer modelling study was carried out on muscle spindles of the cat tenuissimus muscle to examine whether there was any correlation between the functional interaction of putative encoding sites, operated separately by static and dynamic fusimotor neurones, and the topological structure of the preterminal branches of the primary sensory ending. 2. Spindles, whose I a responses to stretch and separate and combined static and dynamic fusimotor stimulation were recorded in physiological experiments, were located in situ. Subsequently the ramifications of the sensory ending were reconstructed histologically, and the topology of the branch tree was used in computer simulations of I a responses to examine the effect of the electronic separation of encoding sites on the static-dynamic interaction pattern. 3. Interactions between separate static and dynamic inputs, manifest in responses to combineed stimulation, were quantified by a coefficient of interaction (Ci) which, by definition, was 1 for strictly linear summation of separate inputs and zero for maximum occlusion between inputs. 4. For the majority of spindles static-dynamic interactions were characterized by pronounced occlusion (C1 < 0.35). In these spindles putative encoding sites (the peripheral heminodes of the branches supplying the intrafusal fibres activated by individual fusimotor efferents) were separated by a minimum conduction path of between three and ten myelinated segments (2-9 nodes of Ranvier). In contrast, significant summation (C1, approximately 0.7) was found in only one spindle. In this case putative encoding sites were separated by a single node. 5. Occlusion was not due to encoder saturation and it could not be accounted for by any other known physiological mechanisms (intrafusal fatigue or unloading). It is therefore attributed to competitive pacemaker interaction between encoding sites which are largely selectively operated by static and dynamic fusimotor efferents. 6. Model simulations of real preterminal-branch tree structures confirmed that short conduction paths between encoding sites were associated with manifest summation, whereas longer minimum conduction paths favoured pronounced occlusion. 7. In the extreme, occlusion could be so pronounced as to give rise to negative values of C1 during critical segments of response cycles. This was associated with lower discharge rates during combined static and dynamic stimulation than the higher of the individual stimulation effects. This phenomenon is referred to as hyperocclusion. Computer simulations demonstrated that hyperocclusion could be accounted for by a slow ionic adaptation process. e.g. by a very slowly activating K+ conductance.

Animals↗
PubMed1999

Characterization of an operon encoding two c-type cytochromes, an aa(3)-type cytochrome oxidase, and rusticyanin in Thiobacillus ferrooxidans ATCC 33020.

Despite the importance of Thiobacillus ferrooxidans in bioremediation and bioleaching, little is known about the genes encoding electron transfer proteins implicated in its energetic metabolism. This paper reports the sequences of the four cox genes encoding the subunits of an aa(3)-type cytochrome c oxidase. These genes are in a locus containing four other genes: cyc2, which encodes a high-molecular-weight cytochrome c; cyc1, which encodes a c(4)-type cytochrome (c(552)); open reading frame 1, which encodes a putative periplasmic protein of unknown function; and rus, which encodes rusticyanin. The results of Northern and reverse transcription-PCR analyses indicated that these eight genes are cotranscribed. Two transcriptional start sites were identified for this operon. Upstream from each of the start sites was a sigma70-type promoter recognized in Escherichia coli. While transcription in sulfur-grown T. ferrooxidans cells was detected from the two promoters, transcription in ferrous-iron-grown T. ferrooxidans cells was detected only from the downstream promoter. The cotranscription of seven genes encoding redox proteins suggests that all these proteins are involved in the same electron transfer chain; a model taking into account the biochemistry and the genetic data is discussed.

Azurin↗