SEARCH · Search PubMed

Results for “repeat interruptions”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources

PubMed2001

Effect of repeated treatment with high doses of selegiline on behaviour, striatal dopaminergic transmission and tyrosine hydroxylase mRNA levels.

The anti-parkinsonian drug selegiline is a monoamine oxidase B (MAO-B) inhibitor and a potential neuroprotective agent which facilitates dopaminergic transmission. Its metabolites (-)-amphetamine and (-)-metamphetamine might contribute to the pharmacological effects as they are also able to increase dopaminergic transmission and in addition might lead to behavioural sensitization after repeated administration. We investigated the effects of acute and repeated treatment with a high dose of selegiline on dopamine overflow in the striatum as well as on behaviour and on tyrosine hydroxylase (TH) mRNA levels in midbrain. Two experiments were performed. In the first one, rats were implanted with microdialysis probes into the striatum and received daily injections of selegiline (10 mg/kg, i.p.) for 1 or 8 days or a single dose of saline. In vivo microdialysis was carried out on days 1, 8 or 17 (after withdrawal of 9 days) to measure dopamine overflow. Motility was measured at the same time. In the second experiment, rats were injected daily with selegiline (10 mg/kg, i.p.) or saline over a time period of 6 weeks or only once before the brains were processed for in situ hybridization with a (35)S-radiolabelled probe for TH. Repeated treatment led to higher levels in motility scores than acute administration after administration of the same dose, indicating behavioural sensitization, which was still manifest after an interruption of 9 days in the supply of selegiline. In contrast, acute administration of selegiline increased dopamine levels to a similar degree as the same dose after subchronic treatment, with or without interruption of 9 days. The dopamine metabolite DOPAC was reduced by more than 50% after acute administration of selegiline and even more so on day 8 by the same dose, after repeated administration. The basal concentrations of dopamine (before challenge with selegiline) were not altered by the repeated administration, whereas the basal concentrations of DOPAC were decreased by more than 80% by the repeated administration of selegiline, suggesting a decrease in dopamine turnover. Acute administration did not have any influence on TH mRNA levels, whereas chronic treatment significantly reduced TH mRNA levels in substantia nigra and ventral tegmental area. In conclusion, repeated administration of selegiline leads to behavioural sensitization independent of altered dopamine levels. In addition, it leads to a decrease, probably due to a down-regulation, of dopamine turnover and tyrosine hydroxylase.

Animals↗

PubMed2001

Effects of interrupted and uninterrupted occlusion of the basilar artery on cerebral blood flow, and on neurological and histological outcome in rats with subarachnoid hemorrhage.

Most neurosurgeons consider temporary vessel occlusion for aneurysmal clipping an effective technique that facilitates dissection between the aneurysm and the parent vessel. It is generally believed that repeated short periods of cerebral ischemia are safer for the brain than a single long episode. The aim of this study was to identify whether interrupted and uninterrupted vessel occlusion differs with regard to changes in brain tissue and cerebral hemodynamics after subarachnoid hemorrhage (SAH). Fifty Spraque Dawley rats (300-350 g) were placed under general anaesthesia and ventilated. The basilar artery was exposed through a transclival approach. Baseline local cerebral blood flow (LCBF) values was measured, and then the basilar artery was punctured, causing subarachnoid hemorrhage (SAH). Group I (n = 24) was subjected to 60 min of interrupted basilar artery occlusion, defined as 5 min of reperfusion after every 10 min of occlusion, group II (n = 26) 60 min of uninterrupted artery occlusion. Three days after completion of the experiment, each rat was neurologically evaluated and decapitated. Coronal brain slices were obtained and stained to assess infarct volume. Immediately after SAH, LCBF fell by 58% in group I, and by 52% in group II. In group I, each ischemic insult brought a similar reduction in LCBF, and after each release of the occlusion there was a rapid rise in flow. In group II, the LCBF values dropped initially and remained at low levels until the end of the study. The 2,3,5 triphenyltetrazolium chloride stained sections showed similar volumes of brainstem infarction in both groups (38.3 +/- 9.2 mm3 vs. 34.3 +/- 8.7 mm3, respectively; p > 0.05). The results suggest that there is no neuroprotective advantage to either interrupted or uninterrupted temporary blockage of blood flow during neurovascular procedures after SAH in the basilar artery region.

Animals↗

PubMed1983

Intracisternal A-particle genes as movable elements in the mouse genome.

We analyzed two functionally defective mouse kappa light chain gene variants previously shown to contain novel insertions of repetitive DNA in their intervening sequences [Hawley, R. G., Shulman, M. J., Murialdo, H., Gibson, D. M. & Hozumi, N. (1982) Proc. Natl. Acad. Sci. USA 79, 7425-7429]. Heteroduplex analysis of the cloned genes shows that the insertions consist of intracisternal A-particle (IAP) genetic elements. Each insertion includes an IAP 5' long terminal repeat (LTR) sequence and extends to a characteristic IAP internal BamHI site where the IAP sequence is interrupted because the mutant genes were cloned from complete BamHI digests of the cellular DNAs. Restriction enzyme mapping indicates that the 5' LTR boundaries of the inserted IAP elements correspond closely to the previously determined rearrangement sites in the mutant genes. The IAP insertions in the two mutants can be distinguished by restriction-site differences and by the fact that one of them contains a deletion that is absent in the other. Nucleotide sequence data are presented for the LTRs of one full-length IAP gene copy randomly selected from a mouse genomic DNA library. These LTRs show many features typical of known integrated retroviral terminal repeat units, and the entire gene is bracketed by short direct repeats within the adjacent cellular DNA. Thus, the findings show that IAP genetic elements can appear in new locations in mouse cellular DNA and suggest that this may occur through a process of proviral insertion.

Animals↗

PubMed1994

Speech rates and turn-taking behaviors of children who stutter and their fathers.

Paralinguistic behaviors, including speech rates and turn-taking behaviors, of boys who stutter and boys who do not stutter and their fathers were investigated. Subjects were 11 boys who stutter (mean age = 5:1) and their fathers and 11 age-matched (+/- 3 months) nonstuttering boys (mean age = 5:1) and their fathers. Spontaneous conversational speech was obtained from each father and son during approximately 45 minutes of videotaped free play in a clinic setting. Measures of overall, articulatory, and dyadic speaking rates, interruptions, response time latencies, and disfluency characteristics were derived using the videotapes and computer-assisted analyses of the acoustic signal from each conversational sample. Two-factor repeated measures ANOVAs were performed on each of the paralinguistic variables for the 11 sets of age-matched father-son pairs. Fathers produced faster speaking rates, higher frequencies of interruptions and shorter response time latencies than sons. No significant differences were found in comparisons of the two groups of fathers or of the two groups of children for any of the paralinguistic behaviors. A significant positive correlation was found between the SSI scores of children who stutter and the dyadic speaking rates of these children and their fathers. Results partially extend those of Kelly and Conture (1992) for mothers and children, but some potentially important differences emerge between fathers' and mothers' (para)linguistic behaviors in interaction with their children.

Age Factors↗

PubMed1987

L1 repeat elements in the human epsilon-G gamma-globin gene intergenic region: sequence analysis and concerted evolution within this family.

We have deduced the sequence of a composite long interspersed repeated DNA in primates and herein describe its relationship to a complex repeat element (L1Heg) located in the interval linking the human epsilon- and G gamma-globin genes. The main element of L1Heg is 3' truncated and interrupted by the insertion of the 3' end of a second L1 element. Transposition of L1Heg into this intergenic locus generated a 62-bp duplication of flanking sequences. In contrast, insertion of the second repeat may have been mediated by homology between donor and target sequences. The main repeat represents a novel class of abundant elements whose sequences have diverged from other rodent and primate LINES approximately 1.3 kb downstream from the 5' terminus of L1Heg. Comparison of L1Heg with the sequences of two other related L1 members revealed a complex set of rearrangements confined within a region that resembles the long terminal repeats of other types of retroposons. The boundaries of conversion-like events were defined on the basis of the clustering of nucleotide sequence variants common to two or more nonallelic 3' L1H elements. Several of these events are apparently initiated or resolved within a common 150-bp region that coincides with the 3' terminus of a pan-mammalian open reading frame. This analysis showed that concerted genetic interactions and random drift both contribute appreciably to sequence variation within this set of L1H members.

Animals↗

PubMed1998

Isolation and structural and genetic analysis of the mouse enkephalin gene and its d(AC/TG)n repeats.

Enkephalins, the endogenous opioids, mediate a wide variety of intercellular communications through ontogeny and their involvement has been suggested in drug addiction and alcohol abuse as well as in various neuropsychiatric disorders. In order to generate a genetic model, we have isolated the mouse enkephalin (mENK) gene, analyzed its regulatory region and compared its structure to the well characterized rat ENK (rENK) gene. We analyzed 2600 bp and found 3 highly homologous regions: The highest level (98%) of positional and sequence homology between mice and rats was in the TATA/proximal regulatory region. This region contains all the inducible regulatory elements (enkCRE1, NF1, AP-2, NFkappaB, etc.) and also an octamer-like element at -543 bp. This high homology is interrupted in both mice and rats by the typically polymorphic d(AC/TG)n and d(TC/GA)n dinucleotide repeats positioned between nucleotides -670 and -950. The position and orientation of these repetitive elements differ substantially in the two species. Genomic PCR analysis of the d(AC/TG)n repeat in various mouse strains, including aberrant behavioral or neurological phenotypes, showed lack of polymorphism at this repeat. The positional and sequence homologies between the rat and the mouse ENK genes decrease in more upstream regions due to the presence of nonhomologues repetititve DNA sequences.

Animals↗

PubMed2005

In-depth sequence analysis of the tomato chromosome 12 centromeric region: identification of a large CAA block and characterization of pericentromere retrotranposons.

We sequenced a continuous 326-kb DNA stretch of a microscopically defined centromeric region of tomato chromosome 12. A total of 84% of the sequence (270 kb) was composed of a nested complex of repeat sequences including 27 retrotransposons, two transposable elements, three MITEs, two terminal repeat retrotransposons in miniature (TRIMs), ten unclassified repeats and three chloroplast DNA insertions. The retrotransposons were grouped into three families of Ty3-Gypsy type long terminal repeat (LTR) retrotransposons (PCRT1-PCRT3) and one LINE-like retrotransposon (PCRT4). High-resolution fluorescence in situ hybridization analyses on pachytene complements revealed that PCRT1a occurs on the pericentromere heterochromatin blocks. PCRT1 was the prevalent retrotransposon family occupying more than 60% of the 326-kb sequence with 19 members grouped into eight subfamilies (PCRT1a-PCRT1h) based on LTR sequence. The PCRT1a subfamily is a rapidly amplified element occupying tens of megabases. The other PCRT1 subfamilies (PCRT1b-PCRT1h) were highly degenerated and interrupted by insertions of other elements. The PCRT1 family shows identity with a previously identified tomato-specific repeat TGR2 and a CENP-B like sequence. A second previously described genomic repeat, TGR3, was identified as a part of the LTR sequence of an Athila-like PCRT2 element of which four copies were found in the 326-kb stretch. A large block of trinucleotide microsatellite (CAA)n occupies the centromere and large portions of the flanking pericentromere heterochromatin blocks of chromosome 12 and most of the other chromosomes. Five putative genes in the remaining 14% of the centromere region were identified, of which one is similar to a transcription regulator (ToCPL1) and a candidate jointless-2 gene.

Base Sequence↗

PubMed1999

Testis-specific murine centrin, Cetn1: genomic characterization and evidence for retroposition of a gene encoding a centrosome protein.

Centrin is a centrosome component in species from yeast to humans. Here, the mouse centrin 1 gene (Cetn1) is analyzed with respect to its genomic structure, chromosome localization, tissue-specific expression, and phylogenetic relationship to the other mouse centrin genes and their human orthologs. Cetn1 is an intronless gene located on chromosome 18A2 that encodes a 172-amino-acid protein with a predicted molecular mass of 19,696 Da (pI 4.61) and all of the structural features common to centrin. Cetn1 possesses the sequence features of an expressed retroposon: the gene lacks introns, the open reading frame is not interrupted by stop codons, and the coding region is flanked by a pair of direct repeats. Reverse transcriptase-polymerase chain reaction and Northern blot analysis demonstrate that Cetn1 expression is limited exclusively to the testis in adult male mice. Cetn1 expression is first seen in the neonatal testis at 14 days postpartum, reaching adult levels by day 17. These observations provide new insight into the regulation, function, and evolutionary history of centrin in higher eukaryotes.

Amino Acid Sequence↗

PubMed1984

Suppression of REM rebound by Pergolide.

A 71 year old retired printer developed idiopathic Parkinson's disease over a period of 3 years. On account of his worsening condition he was admitted to hospital. Following the interruption of his medication the patient developed an akinetic crisis. A 48 hour polysomnogram recording, repeated five times during hospitalization, showed severe sleep deprivation. Treatment with Pergolide alone was then started; and sleep monitoring showed suppression of REM rebound, REM only appearing when the dose of the drug was reduced. It is suggested that REM rebound phenomena produced by sleep deprivation in a Parkinson's disease patient are suppressed by the effect of the dopaminergic agent Pergolide.

Aged↗

PubMed1995

Reflex reversal of apnoeic episodes by electrical stimulation of upper airway in cats.

Respiratory effects of electrical stimulation of the upper airways (UAW) before and during apnoeic episodes induced by nitrogen inhalation were studied in 9 anaesthetized cats. In eupnoeic animals these electrically-evoked reflexes comprise rapid and powerful inspiratory efforts characterized by strong maximal airway occlusion pressures (Pmax = 635 +/- 39 mm H2O) and rapid peak inspiratory flow rates (PIF = 536 +/- 36 ml.sec-1) similar to the sniff-like aspiration reflex elicited mechanically. Electrical stimulation of the UAW mucosa can elicit reflex inspirations and sniff-like aspiration reflexes even during reversible hypoxic apnoea but their intensity and reproducibility are transiently reduced. When repeated adequately, the electrically-induced reflexes can increase the reactivity of respiratory centre and interrupt or terminate apnoeic episodes as do other types of UAW stimulation. Reflex mechanisms and respiratory centre activations seem to be involved in these effects. The results suggest that electrical stimulation of UAW could be useful for testing the respiratory centre reactivity as well as for reflex reversal of apnoeic episodes and restoration of normal breathing in animal experiments and clinico-physiological studies. Such investigation of the role of UAW reflexes in the pathogenesis and therapy of apnoeic syndromes might also be possible by using a cardiostimulator adapted as respiratory pacemaker.

Animals↗

PubMed1981

Unit responses of intralaminar thalamus to midbrain and medullary stimulation and effects of conditioning caudate and hippocampal stimuli.

Single units responding to heterotopic somatic stimuli, on extracellular recording in thalamic intralaminar and neighbouring nuclei, also responding to stimulation of the midbrain tegmentum or the medullary magnocellular reticular formation. Consideration of response latencies suggested that some monosynaptic projections from both midbrain and medulla may be received in nuclei centralis lateralis, centrum medianum-parafascicularis complex, and medial ventralis lateralis. Responses to brainstem of nuclei medialis dorsalis, lateralis posterior were of considerably longer latency. There was no correlation between shortness of latency and following-rate of unit responses; the ability of intralaminar neurons to follow rapidly-repeated brainstem stimuli is inferred to be limited by inhibitory processes rather than by synaptic interruptions in the afferent pathway. Conditioning stimuli to caudate nucleus or hippocampus suppressed most intralaminar responses to midbrain stimuli, the shortest-latency responses included, suggesting that inhibitory effects could be exerted at the thalamic level, perhaps directly on the responsive neurone.

Animals↗

PubMed1989

The promoters and spacers in the rDNAs of the melanogaster species subgroup of Drosophila.

The spacer sequences of rDNAs of members of the melanogaster species subgroup of Drosophila (melanogaster, simulans, mauritiana, teissieri, and yakuba) have been compared. The external transcribed spacers (ETSs; the region encoding the 5' end of the primary transcript, upstream from the 18S sequences) are highly conserved between in D. melanogaster, D. simulans and D. mauritiana, whereas the more distantly related D. yakuba and D. teissieri differ in having apparent deletions of 22 and 27 bp, respectively, in this region. The divergence of nucleotide sequence upstream from the transcription start points is consistent with the established phylogeny of the five species. The sequences between bp positions -47 and +24 from the primary transcription start point show extremely little variation between each species. This is also the case for sequences between the approximate bp positions -140 to -125 and -85 to -70. This could indicate a functional importance not only of the sequences next to the transcription start point, but also of these upstream regions. An array of 240-bp repeats can be found at a comparable distance upstream from the transcription start point in each species. Matrix homology comparisons indicate that for each species not only is the sequence at the primary transcription start point duplicated within the 240-bp repeats as previously reported for D. melanogaster, but that this is part of a longer interrupted duplication which includes a region of strong similarity with the sequence between the approximate positions -105 to -65. This region is contained within one of the regions upstream from the transcription start point that is strongly conserved between the species. This sequence may therefore have functional significance not only for the transcription of the rRNA precursor, but also for transcription of the so-called NTS sequences which is now known to occur. The 240-bp arrays are themselves highly conserved within a species indicating that homogenisation mechanisms are operative. The divergence of these arrays between species is consistent with the phylogenetic tree. The 3' sequences of the primary transcription unit, now known to be RNA-processing sites, are also highly similar between the species. Immediately downstream from these sites there is little homology between the rDNA of the different species, until 95-bp tandem arrays are reached in each case.

Animals↗

PubMed1982

[Intoxication with beta-receptor blockers (author's transl)].

Beta-blockers are increasingly often used with suicidal intent, but are also sometimes swallowed accidentally by small children. Beta-blockers available in the Federal Republic of Germany differ in their pharmacodynamics and pharmacokinetics. After analysing 49 cases of intoxication, no certain relationship was found between the different substances and specific symptoms. Cardiovascular signs such as sinus bradycardia, arrhythmia, hypotension (30 cases), as well as dizziness and drowziness (17) were the most frequent ones. Loss of consciousness and hallucination (13), as well as seizures (3), also occurred frequently. Hypoglycaemia or symptoms due to it (12) were noted especially in young children. In addition to primary removal of the drug, repeated administration of charcoal and sodium sulphate are recommended with most of the drugs for interrupting the enterohepatic circulation. Administration of atropine for bradycardia and hypotension was usually not effective. Dopamine is recommended; glucagon for definite signs of shock. Haemodialysis is indicated only in exceptional instances and is effective for only a few of the drugs. Forced diuresis should not be practised.

Acebutolol↗

PubMed1986

A previously undetected pseudogene in the human alpha globin gene cluster.

The sequence of the DNA between two pseudogenes in the human alpha-like globin gene cluster has been determined. Comparison of this sequence with sequences from other alpha-like globin gene clusters revealed another pseudogene, psi alpha 2, between the previously recognized pseudogenes zeta 1 and psi alpha 1. Therefore, the human alpha-like globin gene family is organized 5'-zeta 2-zeta 1-psi alpha 2-psi alpha 1-alpha 2-alpha 1-3'. The new pseudogene psi alpha 2 is very close to zeta 1, beginning only 65 base pairs 3' to the polyadenylation site of zeta 1. The first exon and the first intron of psi alpha 2 are interrupted by large inserts which are flanked by short (6 to 8 base pairs) direct repeats. The pseudogene psi alpha 2 lacks a promoter for transcription by RNA polymerase II, the first exon is highly divergent, one splice site is mutated, and five different frameshift mutations have occurred in the coding regions. Thus psi alpha 2 cannot encode a globin polypeptide. This pseudogene was not recognized in previous hybridization analyses of the human alpha-like globin gene cluster, and our discovery of it by sequence analysis suggests that divergent copies of a large number of genes may comprise a substantial fraction of the slowly renaturing DNA of mammalian genomes.

Base Sequence↗

PubMed1995

A subset of macrophages located along the basement membrane ("lining cells") is a characteristic histopathological feature of psoriasis.

In this paper, we describe the immunophenotype and ultrastructure of a new macrophage subpopulation present in inflamed but not in normal human skin. In biopsy material from patients with psoriasis (n = 4), atopic dermatitis (n = 4), and positive patch test reactions (n = 4), spindle-shaped macrophages located along the basement membrane were detected staining positive for CD11c (LeuM5 high, Ki-M1 low), CD68 (Ki-M6 low), and Ki-M8 (low). This subpopulation was most prominent in psoriasis, where a median of 34 macrophages neighbored 100 basal keratinocytes, thus covering about 80% of the dermoepidermal junction. The numbers of atopic and positive patch test reactions were 11 and 13, respectively, accounting for about 20% of the dermoepidermal junction. Transmission electron microscopy revealed an electron-lucent nucleus with dense deposits of chromatin along the nuclear membrane. Interruptions of the integrity of the basement membrane neighboring these cells were also seen. We repeatedly observed parts of basal keratinocytes merging through these openings and macrophages exhibiting cytoplasmic extentions directed toward the porus. Our observations suggest vigorous interactions between macrophages and basal keratinocytes and support the hypothesis that these interactions are an important regulatory event in the pathogenesis of psoriasis.

Antigens, CD↗

PubMed2004

Increased intake of fruit and vegetables and a low-fat diet, with and without low-fat plant sterol-enriched spread consumption: effects on plasma lipoprotein and carotenoid metabolism.

BACKGROUND: Regular intake of plant sterol (phytosterol)-enriched foods enhances the cholesterol lowering effect of diets. One side effect associated with plant sterol consumption is a modest reduction in plasma carotenoid concentrations. This study investigated the effect of consuming a low-fat National Cholesterol Education Programme (NCEP) Step 1 diet, including a low-fat plant sterol ester (PSE)-enriched spread on cholesterol metabolism to determine if specific dietary advice to increase daily fruit and vegetable intake could prevent reduced plasma carotenoid concentrations. MATERIALS AND METHODS: In this randomised, crossover double-blind trial, 48 hypercholesterolaemic men received 21 g day(-1) of a low-fat PSE-enriched spread or placebo for 3 weeks, interrupted by 3 weeks washout. Individuals also adhered to a NCEP Step 1 diet and repeated 3-day food diaries monitored adherence. Specific advice was provided to increase dietary fruit and vegetable intakes. Fasting blood samples were collected at pre- and post-intervention for lipoprotein and carotenoid analysis. RESULTS: Plasma total and low-density lipoprotein (LDL) cholesterol concentrations were significantly (P <0.05) reduced, by 4.6 and 7.1%, respectively, after the PSE-enriched low-fat spread. Plasma apo B concentrations were significantly (P <0.0005) lower after the PSE spread. PSE consumption was also associated with significantly (P <0.05) lower total plasma beta-carotene concentrations, but this change was not significant after lipid standardisation. PSE consumption had no effect on retinol, alpha-carotene, gamma-tocopherol, alpha-tocopherol, lutein, zeaxanthin, beta-crypyoxanthin or lycopene concentrations. CONCLUSION: Dietary advice to increase daily fruit and vegetable consumption may be effective in preventing a reduction in plasma carotenoid concentrations previously associated with PSE consumption. Further, PSE incorporated in a low-fat spread and consumed as part of a NCEP Step 1 diet are effective in reducing total and LDL cholesterol.

Adult↗

PubMed1998

Transfer of Tn5385, a composite, multiresistance chromosomal element from Enterococcus faecalis.

Tn5385 is a ca. 65-kb element integrated into the chromosomes of clinical Enterococcus faecalis strains CH19 and CH116. It confers resistance to erythromycin, gentamicin, mercuric chloride, streptomycin, tetracycline-minocycline, and penicillin via beta-lactamase production. Tn5385 is a composite structure containing regions previously found in staphylococcal and enterococcal plasmids. Several transposons and transposon-like elements within Tn5385 have been identified, including conjugative transposon Tn5381, composite transposon Tn5384, and elements indistinguishable from staphylococcal transposons Tn4001 and Tn552. The divergent regions of Tn5385 are linked by a series of insertion sequence (IS) elements (IS256, IS257, and IS1216) of staphylococcal and enterococcal origin. The ends of Tn5385 consist of directly repeated copies of enterococcal IS1216. Within the chromosomes of strains CH19 and CH116, Tn5385 has interrupted an open reading frame with substantial homology to previously described alkyl hydrogen peroxide reductase genes. Segments of this open reading frame in both CH19 and CH116 have been deleted, but the amount of deleted DNA differs for the two insertions. Transfer of Tn5385 from both donors into E. faecalis recipients occurs at a low frequency. Two types of transconjugants have been identified. In one type, the target alkyl hydrogen peroxide reductase open reading frame has been deleted, and sequences flanking Tn5385 in the respective donors are carried over to the transconjugants. These data suggest that the mechanism of Tn5385 insertion into the recipient chromosome in these transconjugants was recombination across flanking regions in the donors and homologous sequences in the recipients. The second type of transconjugant appears to have resulted from excision of Tn5385 from the CH19 chromosome by recombination across the terminal IS1216 elements and insertion into the recipient chromosome by recombination across Tn5381 (within Tn5385) and a previously transferred Tn5381 copy in the recipient chromosome. These data confirm that Tn5385 is a composite structure with genetic material from diverse genera and suggest that it is a functional transposon. They also suggest that chromosomal recombination is a mechanism of genetic exchange in enterococci.

Base Sequence↗

PubMed1998

Homology-dependent maternal inhibition of developmental excision of internal eliminated sequences in Paramecium tetraurelia.

Thousands of single-copy internal eliminated sequences (IESs) are excised from the germ line genome of ciliates during development of the polygenomic somatic macronucleus, following sexual events. Paramecium IESs are short, noncoding elements that frequently interrupt coding sequences. No absolutely conserved sequence element, other than flanking 5'-TA-3' direct repeats, has been identified among sequenced IESs; the mechanisms of their specific recognition and precise elimination are unknown. Previous work has revealed the existence of an epigenetic control of excision. It was shown that the presence of one IES in the vegetative macronucleus results in a specific inhibition of the excision of the same element during the development of a new macronucleus, in the following sexual generation. We have assessed the generality and sequence specificity of this transnuclear maternal control by studying the effects of macronuclear transformation with 13 different IESs. We show that at least five of them can be maintained in the new macronuclear genome; sequence specificity is complete both between genes and between different IESs in the same gene. In all cases, the degree of excision inhibition correlates with the copy number of the maternal IES, but each IES shows a characteristic inhibition efficiency. Short internal IES-like segments were found to be excised from two of the IESs when excision between normal boundaries was inhibited. Available data suggest that the sequence specificity of these maternal effects is mediated by pairing interactions between homologous nucleic acids.

Animals↗