Search PubMed⌕ Search

Biomedical subjects

H Niki

Publications and source records attributed to H Niki.

At least 55 records · Page 3Linked to original sources
PubMed1996

Carboxyl terminal region of the MukB protein in Escherichia coli is essential for DNA binding activity.

The purified MukB protein of Escherichia coli has DNA binding activity and nucleotide binding activity. We have isolated a mutation, mukB1013, causing a substitution of valine at position 1379 to leucine. This mutant MukB protein was defective for DNA binding, while the ATP binding activity remained unaffected. A truncated MukB protein that is short of 109 amino acids from the C-terminus failed to bind DNA.

Adenosine Triphosphate↗
PubMed1996

Identification of two new genes, mukE and mukF, involved in chromosome partitioning in Escherichia coli.

We have previously reported that the MukB protein is essential for chromosome partitioning in Escherichia coli and that mukB mutants produce anucleate cells and are temperature-sensitive for colony formation. The mukB gene maps at 21 min on the E. coli chromosome and smtA-mukF-mukE-mukB genes might comprise an operon, which is transcribed in a clockwise direction. Here, we report that mukF and mukE null mutants are both temperature-sensitive for colony formation and produce anucleate cells even at the permissive temperature. These phenotypes are the same as those observed in the mukB null mutant. The primary sequence of MukF includes a leucine zipper structure and an acidic domain. Mutational analysis revealed that both are required for MukF function. When the MukF protein was overproduced in the wild-type strain, anucleate cells were produced. In contrast, overproduction of either MukE or MukB did not cause the defect. In null mutants for the mukF, mukE, and mukB genes, the synchronous initiation of chromosome replication was not affected. The mini-F plasmid was as stably maintained in these mutants as in the wild-type strain. These results indicate that the MukF, MukE, and MukB proteins are involved in the chromosome partitioning steps, but are not required for mini-F plasmid partitioning.

Amino Acid Sequence↗
PubMed1996

Radial maze performance, open-field and elevated plus-maze behaviors in Fyn-kinase deficient mice: further evidence for increased fearfulness.

Fyn-deficient mice produced by inserting the beta-galactosidase gene (lacZ) into the fyn gene locus were tested in a radial maze, an open field and an elevated plus-maze. In the radial maze, the homozygous Fyn-deficient (fynz/fynz) mice showed no impairment in spatial learning, although they showed a stronger avoidance tendency for those arms located closer to the experimenter during pretraining (adaptation). In the open-field test, the fynz/fynz mice defecated more frequently in the bright condition than did the +/fynz mice, and they were less active during the first 10-min test period than the +/fynz mice. In addition, the temporal pattern of locomotor activity for fynz/fynz mice was altered by changing the illumination while the pattern for +/fynz mice remained relatively unchanged. Scores reflecting the fear-response in the elevated plus-maze were higher in the fynz/fynz mice. These results indicate that Fyn deficiency increased fear-response, but did not impair spatial learning in the radial maze. It is suggested that we should take account of effects of emotional factors in the learning experiment using mutant mice.

Animals↗
PubMed1996

RNase E polypeptides lacking a carboxyl-terminal half suppress a mukB mutation in Escherichia coli.

We have isolated suppressor mutants that suppress temperature-sensitive colony formation and anucleate cell production of a mukB mutation. A linkage group (smbB) of the suppressor mutations is located in the rne/ams/hmp gene encoding the processing endoribonuclease RNase E. All of the rne (smbB) mutants code for truncated RNase E polypeptides lacking a carboxyl-terminal half. The amount of MukB protein was higher in these rne mutants than that in the rne+ strain. These rne mutants grew nearly normally in the mukB+ genetic background. The copy number of plasmid pBR322 in these rne mutants was lower than that in the rne+ isogenic strain. The results suggest that these rne mutations increase the half-lives of mukB mRNA and RNAI of pBR322, the antisense RNA regulating ColE1-type plasmid replication. We have demonstrated that the wild-type RNase E protein bound to polynucleotide phosphorylase (PNPase) but a truncated RNase E polypeptide lacking the C-terminal half did not. We conclude that the C-terminal half of RNase E is not essential for viability but plays an important role for binding with PNPase. RNase E and PNPase of the multiprotein complex presumably cooperate for effective processing and turnover of specific substrates, such as mRNAs and other RNAs in vivo.

Bacterial Proteins↗
PubMed1995

Characterization of the smtA gene encoding an S-adenosylmethionine-dependent methyltransferase of Escherichia coli.

The mukB operon is located at 21 min on the Escherichia coli chromosome and seems to consist of four genes, orf30 (smtA), mukF, mukE, and mukB. Based on sequence similarity, the promoter-proximal gene, orf30 (smtA), could encode an S-adenosylmethionine-dependent methyltransferase. The smtA gene is not essential for cell growth and its expression is positively regulated by H-NS, an Escherichia coli histone-like protein.

Amino Acid Sequence↗
PubMed1995

Escherichia coli FtsH is a membrane-bound, ATP-dependent protease which degrades the heat-shock transcription factor sigma 32.

Escherichia coli FtsH is an essential integral membrane protein that has an AAA-type ATPase domain at its C-terminal cytoplasmic part, which is homologous to at least three ATPase subunits of the eukaryotic 26S proteasome. We report here that FtsH is involved in degradation of the heat-shock transcription factor sigma 32, a key element in the regulation of the E. coli heat-shock response. In the temperature-sensitive ftsH1 mutant, the amount of sigma 32 at a non-permissive temperature was higher than in the wild-type under certain conditions due to a reduced rate of degradation. In an in vitro system with purified components, FtsH catalyzed ATP-dependent degradation of biologically active histidine-tagged sigma 32. FtsH has a zinc-binding motif similar to the active site of zinc-metalloproteases. Protease activity of FtsH for histidine-tagged sigma 32 was stimulated by Zn2+ and strongly inhibited by the heavy metal chelating agent o-phenanthroline. We conclude that FtsH is a novel membrane-bound, ATP-dependent metalloprotease with activity for sigma 32. These findings indicate a new mechanism of gene regulation in E. coli.

ATP-Dependent Proteases↗
PubMed1995

Enhanced susceptibility of audiogenic seizures in Fyn-kinase deficient mice.

Mice with a mutation in fyn genes were examined for their susceptibility to acoustically primed audiogenic seizures. Homozygous mutant (fynz/fynz) mice were significantly more likely to have seizures and to show the stronger seizure syndrome (clonus). These results indicate that the susceptibility of acoustically primed audiogenic seizures is enhanced in the Fyn kinase deficient mice.

Animals↗
PubMed1994

Two mutant alleles of mukB, a gene essential for chromosome partition in Escherichia coli.

The MukB protein is essential for chromosome partitioning in Escherichia coli and consists of 1484 amino acid residues (170 kDa). We have determined the base changes at the mutated sites of the mukB106 mutant and a newly isolated mutant, mukB33. These mutant mukB genes were each found to carry a single base-pair transition which leads to an amino acid substitution; a serine residue at position 33 was changed to phenylalanine in the case of mukB106, and an aspartic acid residue at position 1201 was changed to asparagine in the case of mukB33.

Alleles↗
PubMed1994

Characterization of translucent segments observed in an smbA mutant of Escherichia coli.

The smbA gene of Escherichia coli is essential for cell proliferation. The smbA2 mutant shows cold-sensitive colony formation at 22 degrees C. A novel morphological phenotype, formation of a translucent segment at midcell or at a cell pole, was observed by phase-contrast microscopy at a high frequency in the smbA2 mutant cells incubated in L medium lacking NaCl at 22 degrees C, but not observed in L medium containing 1% NaCl or 20% sucrose at the same temperature. No translucent segment was observed in the wild-type cells in any of the media used. Electron microscopic observation revealed that the translucent segments resulted from the enlargement of a periplasmic space by separation of the inner membrane from the peptidoglycan layer and the outer membrane.

Bacterial Proteins↗
PubMed1994

Spatial selectivity of go/no-go neurons in monkey prefrontal cortex.

We examined single-unit activity in the inferior prefrontal cortex during a visual go/no-go discrimination task under maintained visual fixation. The monkeys had to base their response on either the color, shape, or position of a discriminative cue, and the relevant task condition was indicated by the color of the fixation spot. We analyzed the spatial selectivity of 128 go/no-go neurons showing a marked differential cue-period activity that depended on whether the stimulus signaled a go or no-go response. Most of these neurons (n = 106, 83%) showed asymmetry between their responses to stimuli in the contralateral and ipsilateral visual fields. Seventy-seven of these neurons had a contralateral preferential field, and 29 had an ipsilateral preferential field. These results show that in many inferior prefrontal neurons a degree of differentiation in their responses to go and no-go stimuli depends on the cue positions, and that the coding of behavioral meaning is carried out mainly in the contralateral hemisphere.

Animals↗
PubMed1994

Encoding of behavioral significance of visual stimuli by primate prefrontal neurons: relation to relevant task conditions.

Single-unit activity was recorded from the inferior dorsolateral prefrontal cortex of two monkeys while they performed a symmetrically rewarded go/no-go discrimination task. Three different task conditions were used in which the monkeys had to base their response on (1) the color, or (2) the shape, or (3) the position of a cue that was presented during fixation of a light spot. The colors of the fixation spot informed the monkeys which condition was relevant. The monkeys had to make an immediate release (go) or a delayed release (no-go) at the time of the fixation color change (imperative stimulus) depending on the currently relevant condition and the discriminative cue previously presented. The effect of changing the relevant condition on neuronal responses to the discriminative cue was analyzed. Out of 328 neurons tested in two or three conditions, 249 responded differentially at the cue period depending on the particular behavioral meaning of the stimulus (go or no-go) in at least one of the task conditions. This differential cue-period activity was examined across the different task conditions: the majority of neurons (111/154, 72%) showed such activity in all three conditions. In the remaining 43 neurons (28%) the differential activity was observed in two conditions (27/154, 18%) or in one condition (16/154, 10%). A few neurons (n = 7) showed feature-specific cue-period activity. In addition, 27 neurons displayed condition-dependent anticipatory activity prior to the cue onset. It is suggested that neurons in the inferior dorsolateral prefrontal cortex may participate in the conversion of sensory information from different visual channels into behavioral information (information on the upcoming response).

Animals↗
PubMed1994

New killing system controlled by two genes located immediately upstream of the mukB gene in Escherichia coli.

The nucleotide sequence was determined of the region upstream of the mukB gene of Escherichia coli. Two new genes were found, designated kicA and kicB (killing of cell); the gene order is kicB-kicA-mukB. Promoter activities were detected in the regions immediately upstream of kicB and kicA, but not in front of mukB. Gene disruption experiments revealed that the kicA disruptant was nonviable, but the kicB-disrupted mutant and the mutant lacking both the kicB and kicA genes were able to grow. When kicA disruptant cells bearing a temperature-sensitive replication plasmid carrying the kicA+ gene were grown at 30 degrees C and then transferred to 42 degrees C, the mutant cells gradually lost colony-forming ability, even in the presence of a mukB+ plasmid. Rates of protein synthesis, but not of RNA or DNA synthesis, fell dramatically during incubation at 42 degrees C. These results suggested that the kicB gene encodes a killing factor and the kicA gene codes for a protein that suppresses the killing function of the kicB gene product. It was also demonstrated that KicA and KicB can function as a post-segregational killing system, when the genes are transferred from the E. coli chromosome onto a plasmid.

Amino Acid Sequence↗
PubMed1994

Multicopy suppressors, mssA and mssB, of an smbA mutation of Escherichia coli.

We have isolated and characterized two multicopy suppressors, mssA and mssB, which suppress the cold-sensitive growth phenotype of the smbA2 mutant of Escherichia coli. The mssA gene is located immediately upstream of the rpsA gene (20.5 min). MssA protein was found to be related to nucleoside monophosphate kinases. The mssB gene was found to be identical to the deaD gene (69 min), which encodes a putative RNA helicase. The SmbA protein belongs to the aspartokinase family and probably represents a new, fourth aspartokinase species in E. coli. Expression of the smbA gene is essential for cell growth. The smbA2 mutant shows a pleiotropic phenotype characterized by cold-sensitive growth, hypersensitivity to the detergent sodium dodecyl sulfate, and formation of a translucent segment at midcell or at a pole of the cell when grown at 22 degrees C. In addition, some cellular proteins were either increased or decreased in amount in the smbA2 mutant. SmbA may be a regulatory factor in the expression of a battery of genes. MssA and MssB might also relate to the expression of some of these genes. Multiple copies mssA and mssB suppressed the various phenotypic features of the smbA2 mutant to various extents, suppressing the cold-sensitive growth completely.

Amino Acid Sequence↗
PubMed1994

Increased fearfulness of Fyn tyrosine kinase deficient mice.

Fyn-deficient mice were produced by inserting the beta-galactosidase gene (lacZ) into the fyn gene locus. The homozygously Fyn kinase-deficient (fynz/fynz) mice exhibited stronger light aversion in the light-dark choice test and higher fear-response scores in the novelty preference and passive avoidance tests than did the heterozygously Fyn-deficient (+/fynz) mice. These results indicate that fynz/fynz mice are hyperresponsive to fear-inducing stimuli.

Animals↗
PubMed1994

Cloning, sequencing, and characterization of multicopy suppressors of a mukB mutation in Escherichia coli.

The mukB gene codes for a 177 kDa protein, which might be a candidate for a force-generating enzyme in chromosome positioning in Escherichia coli. The mukB106 mutant produces normal-sized, anucleate cells and shows a temperature-sensitive colony formation. To identify proteins interacting with the MukB protein, we isolated three multicopy suppressors (msmA, msmB, and msmC) to the temperature-sensitive colony formation of the mukB106 mutation. The msmA gene, which could not suppress the production of anucleate cells, was found to be identical to the dksA gene. The msmB and msmC genes suppressed the production of anucleate cells as well as the temperature-sensitive colony formation. However, none of them could suppress both phenotypes in a mukB null mutation. DNA sequencing revealed that the msmB gene was identical to the cspC gene and that the msmC gene had not been described before. A homology search revealed that the amino acid sequences of both MsmB and MsmC possessed high similarity to proteins containing the cold-shock domain, such as CspA of E. coli and the Y-box binding proteins of eukaryotes; this suggests that MsmB and MsmC might be DNA-binding proteins that recognize the CCAAT sequence. Hence, the msmB and msmC genes were renamed cspC and cspE, respectively. Possible mechanisms for suppression of the mukB106 mutation are discussed.

Amino Acid Sequence↗
PubMed1993

Presence and possible involvement of Ca/calmodulin-dependent protein kinases in insulin release from the rat pancreatic beta cell.

Roles of Ca/calmodulin-dependent protein kinase II (Ca/CaM kinase II) and myosin light chain kinase (MLCK) in insulin release from rat pancreatic islets were investigated. Western blotting using polyclonal antibody to Ca/CaM kinase II suggested the presence of this kinase in the pancreatic islets. Extracts of pancreatic islets phosphorylated exogenous myosin light chain, which was inhibited by ML-9, an inhibitor of MLCK. KN-62 and KN-93, inhibitors of Ca/CaM kinase II, and ML-9 at microM concentrations inhibited insulin release stimulated by glucose or high K+. KN-62 and KN-93, but not ML-9, inhibited insulin release increased by glucose and forskolin, an activator of adenylate cyclase. These inhibitors had no effect on insulin release evoked by 12-O-tetradecanoyl phorbol-13-acetate, an activator of Ca(2+)-sensitive, diacylglycerol-dependent protein kinase. These results suggest that Ca/CaM kinase II and MLCK may participate in the control of insulin release.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

Modification of the responses of hippocampal neurons in the monkey during the learning of a conditional spatial response task.

In order to analyze the function of the hippocampus in learning, the activity of single neurons was recorded while monkeys learned a task of the type known to be impaired by damage to the hippocampus. In the conditional response task, the monkey had to learn to make one response when one stimulus was shown, and a different response when a different stimulus was shown. It had previously been shown that there are neurons in the hippocampal formation that respond in this task, to, for example, a combination of a particular visual stimulus that had been associated in previous learning with a particular behavioral response. In the present study, it was found that during such conditional response learning, the activity of 22% of the neurons in the hippocampus and parahippocampal gyrus with activity specifically related to the task altered their responses so that their activity, which was initially equal to the two new stimuli, became progressively differential to the two stimuli when the monkey learned to make different responses to the two stimuli. These changes occurred for different neurons just before, at, or just after the time when the monkey learned the correct response to make to the stimuli. In addition to these neurons, which had differential responses that were sustained for as long as the recordings continued, another population of neurons (45% of those with activity specifically related to the task) developed differential activity to the two new stimuli, yet showed such differential responses transiently for only a small number of trials at about the time when the monkey learned. These findings are consistent with the hypothesis that some synapses on hippocampal neurons modify during this type of learning so that some neurons come to respond to particular stimulus-response associations that are being learned. Further, the finding that many hippocampal neurons started to reflect the new learning, but then stopped responding differentially (the transient neurons), is consistent with the hypothesis that the hippocampal neurons with large sustained changes in their activity inhibited the transient neurons, which then underwent reverse learning, thus providing a competitive mechanism by which not all neurons are allocated to any one learned association or event.

Action Potentials↗