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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

The Escherichia coli FtsH protein is a prokaryotic member of a protein family of putative ATPases involved in membrane functions, cell cycle control, and gene expression

The ftsH gene is essential for cell viability in Escherichia coli. We cloned and sequenced the wild-type ftsH gene and the temperature-sensitive ftsH1(Ts) gene. It was suggested that FtsH protein was an integral membrane protein of 70.7 kDa (644 amino acid residues) with a putative ATP-binding domain. The ftsH1(Ts) gene was found to have two base substitutions within the coding sequence corresponding to the amino acid substitutions Glu-463 by Lys and Pro-587 by Ala. Homology search revealed that an approximately 200-amino-acid domain, including the putative ATP-binding sequence, is highly homologous (35 to 48% identical) to the domain found in members of a novel, eukaryotic family of putative ATPases, e.g., Sec18p, Pas1p, CDC48p, and TBP-1, which function in protein transport pathways, peroxisome assembly, cell division cycle, and gene expression, respectively. Possible implications of these observations are discussed.

Topology and subcellular localization of FtsH protein in Escherichia coli

FtsH protein in Escherichia coli is an essential protein of 70.7 kDa (644 amino acid residues) with a putative ATP-binding sequence. Western blots (immunoblots) of proteins from fractionated cell extracts and immunoelectron microscopy of the FtsH-overproducing strain showed exclusive localization of the FtsH protein in the cytoplasmic membrane. Most of the FtsH-specific labeling with gold particles was observed in the cytoplasmic membrane and the adjacent cytoplasm; much less was observed in the outer membrane and in the bulk cytoplasm. Genetic analysis by TnphoA insertions into ftsH revealed that the 25- to 95-amino-acid region, which is flanked by two hydrophobic stretchs, protrudes into the periplasmic space. From these results, we concluded that FtsH protein is an integral cytoplasmic membrane protein spanning the membrane twice and that it has a large cytoplasmic carboxy-terminal part with a putative ATP-binding domain. The average number of FtsH molecules per cell was estimated to be approximately 400.

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.

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.

E.coli MukB protein involved in chromosome partition forms a homodimer with a rod-and-hinge structure having DNA binding and ATP/GTP binding activities

mukB mutants of Escherichia coli are defective in the correct partitioning of replicated chromosomes. This results in the appearance of normal-sized anucleate (chromosome-less) cells during cell proliferation. Based on the nucleotide sequence of the mukB gene, the MukB protein of 177 kDa was predicted to be a filamentous protein with globular domains at the ends, and also having DNA binding and nucleotide binding abilities. Here we present evidence that the purified MukB protein possesses these characteristics. MukB forms a homodimer with a rod-and-hinge structure having a pair of large, C-terminal globular domains at one end and a pair of small, N-terminal globular domains at the opposite end; it tends to bend at a middle hinge site of the rod section. Chromatography in a DNA-cellulose column and the gel retardation assay revealed that MukB possesses DNA binding activity. Photoaffinity cross-linking experiments showed that MukB binds to ATP and GTP in the presence of Zn2+. Throughout the purification steps, acyl carrier protein was co-purified with MukB.

Identification and characterization of the smbA gene, a suppressor of the mukB null mutant of Escherichia coli

The mukB gene encodes a protein involved in chromosome partitioning in Escherichia coli. To study the function of this protein, we isolated from the temperature-sensitive mukB null mutant and characterized 56 suppressor mutants which could grow at 42 degrees C. Ten of the mutants also showed cold-sensitive growth at 22 degrees C. Using one of the cold-sensitive mutants as host, the wild type of the suppressor gene was cloned. The cloned suppressor gene complemented all of the 56 suppressor mutations. DNA sequencing revealed the presence of an open reading frame of 723 bp which could encode a protein of 25,953 Da. The gene product was indeed detected. The previously undiscovered gene, named smbA (suppressor of mukB), is located at 4 min on the E. coli chromosome, between the tsf and frr genes. The smbA gene is essential for cell proliferation in the range from 22 to 42 degrees C. Cells which lacked the SmbA protein ceased macromolecular synthesis. The smbA mutants are sensitive to a detergent, sodium dodecyl sulfate, and they show a novel morphological phenotype under nonpermissive conditions, suggesting a defect in specific membrane sites.

Characterization of high molecular weights of complexes and polymers of cytoplasmic proteins in Escherichia coli

To search for filamentous polymers of cytoplasmic proteins of Escherichia coli, high molecular weights (> 670 kDa) of protein complexes of cell extracts were fractionated by gel filtration and ion-exchange column chromatography. Proteins of 100, 77 and 52 kDa were co-purified. The 100- and 52-kDa proteins were identified to be pyruvate dehydrogenase and lipoamide dehydrogenase, respectively, by determining the N-terminal amino acid sequences. Experimental results indicate that the 77-kDa protein is identical to dihydrolipoamide acyltransferase. The 100-kDa protein was found to be identical to the 100-kDa protein described by Tomioka (1991), and was related to the formation of filaments and sheets in the presence of 100 mM KCl. However, neither long filaments nor sheets were observed in our sample containing these enzymes, which was not consistent with Tomioka's conclusion. Another 100-kDa protein which forms spirosome-like particles was purified and identified to be alcohol dehydrogenase based on the N-terminal sequence.

Lupus nephritis associated with bacterial panperitonitis and lung alveolar hemorrhage

A 36-year-old woman was admitted to the hospital with the diagnosis of nephrotic syndrome due to lupus nephritis. The patient had panperitonitis caused by Staphylococcus aureus as a complication, and an emergency laparotomy was performed. After the operation, the patient developed a massive lung alveolar hemorrhage. Methylprednisolone pulse therapy showed a marked effect on the lung hemorrhage. It is known that lung alveolar hemorrhages associated with systemic lupus erythematosus have a very high mortality; the present case is relatively rare because of the good response to steroid pulse therapy.

Escherichia coli mutant Y16 is a double mutant carrying thermosensitive ftsH and ftsI mutations

The Escherichia coli mutant Y16, which shows thermosensitive colony formation and filamentation with reduced amounts of penicillin-binding protein 3 (PBP3), has mutations in the ftsI gene encoding PBP3 and in the ftsH gene. The ftsI mutation markedly reduces the amount of PBP3 at 42 degrees C, whereas the amount of the ftsH single mutant is slightly reduced.

Partitioning of a mini-F plasmid into anucleate cells of the mukB null mutant

The partition-proficient mini-F plasmid pXX325 was stably maintained in the mukB null mutant, which is defective in chromosome partitioning into the two daughter cells. In the null mutant, the plasmid was partitioned into both nucleate and anucleate daughter cells, independently of host chromosomes.

Eosinophilic peritonitis responding to treatment with glycyrrhizin

A 63-year-old man with diabetes mellitus for 15 years was admitted to our hospital in 1990 because of end-stage renal failure. Five days after beginning continuous ambulatory peritoneal dialysis (CAPD) he developed an eosinophilic peritonitis (EP). With protein loss in the dialysate and a decreased serum albumin level, the patient developed ankle edema. The patient was treated with glycyrrhizin, and his EP resolved. It is suggested that an allergic background may play an important role in the development of EP in patients on CAPD.

Structure and function of the ftsH gene in Escherichia coli

The ftsH mutant Y16 shows thermosensitive filamentation with reduced amounts of penicillin-binding protein 3 (PBP3) (Ferreira et al., 1987). Genetic analysis, however, showed that the lethality of the ftsH mutation was not due to a lack of PBP3 activity alone. The ftsH gene was cloned and sequenced and the FtsH protein was deduced to be a membrane protein of 70.7 kDa which has an ATP-binding domain. Highly significant homology of amino acid sequence was observed between FtsH protein and two eukaryotic proteins, yeast Saccharomyces cerevisiae Sec 18p and its mammalian homologue NSF, which are involved in protein transport pathways. This suggests that FtsH protein may act for translocation of specific proteins including PBP3 and at least one other additional protein essential for cell growth. Suppressor mutants of Y16, which were able to grow at 42 degrees C, were isolated, and the suppressor mutations (sfh) were mapped to 16 min. A wild type chromosomal fragment able to complement the sfh mutations was cloned. We also identified another gene (ftsJ) affecting cell division in the region upstream of the ftsH gene.

Mutants defective in chromosome partitioning in E. coli

Recent experimental results suggest that replicated daughter chromosomes (nucleoids) in Escherichia coli move non-progressively and abruptly at an early stage of the D (division) period from midcell toward the cell quarter positions, which will become the centres of the daughter cells. The chromosome positioning at the quarter positions was found to be controlled by the muk gene products. In muk mutants, normal size anucleate cells are spontaneously produced during cell division. The mukA gene is identical to the tolC gene encoding an outer membrane protein. The mukB gene codes for a 177-kDa protein. The amino acid sequence of the MukB protein deduced for the nucleotide sequence suggests that the MukB protein has five characteristic secondary structure domains: an amino-terminal globular domain containing a consensus sequence binding with ATP or another nucleotide. The central region of the protein consists of two alpha-helical coiled-coil domains and one globular domain. A carboxyl-terminal globular domain is rich in cysteine and positively charged residues arginine and lysine. Two MukB protein molecules might form a homodimer in the coiled-coil regions. The predicted secondary structure of the MukB protein suggests that the protein provides the force required for the positioning of nucleoids from midcell toward the cell quarters. The mukC and mukD genes are located at 88 and 41 min of the chromosome map, respectively.

The new gene mukB codes for a 177 kd protein with coiled-coil domains involved in chromosome partitioning of E. coli

An Escherichia coli temperature sensitive mutant which produces spontaneously normal size anucleate cells at low temperature was isolated. The mutant is defective in a previously undescribed gene, named mukB, located at 21 min on the chromosome. The mukB gene codes for a large protein (approximately 180 kd). A 1534 amino acid protein (176,826 daltons) was deduced from the nucleotide sequence of the mukB gene. Computer analysis revealed that the predicted MukB protein has distinct domains: an amino-terminal globular domain containing a nucleotide binding sequence, a central region containing two alpha-helical coiled-coil domains and one globular domain, and a carboxyl-terminal globular domain which is rich in Cys, Arg and Lys. A 180 kd protein detected in wild-type cell extracts by electrophoresis is absent in mukB null mutants. Although the null mutants are not lethal at low temperature, the absence of MukB leads to aberrant chromosome partitioning. At high temperature the mukB null mutants cannot form colonies and many nucleoids are distributed irregularly along elongated cells. We conclude that the MukB protein is required for chromosome partitioning in E. coli.

New topoisomerase essential for chromosome segregation in E. coli

The nucleotide sequence of the parC gene essential for chromosome partition in E. coli was determined. The deduced amino acid sequence was homologous to that of the A subunit of gyrase. We found another new gene coding for about 70 kd protein. The gene was sequenced, and the deduced amino acid sequence revealed that the gene product was homologous to the gyrase B subunit. Mutants of this gene were isolated and showed the typical Par phenotype at nonpermissive temperature; thus the gene was named parE. Enhanced relaxation activity of supercoiled plasmid molecules was detected in the combined crude cell lysates prepared from the ParC and ParE overproducers. A topA mutation defective in topoisomerase I could be compensated by increasing both the parC and the parE gene dosage. It is suggested that the parC and parE genes code for the subunits of a new topoisomerase, named topo IV.

Linear multimer formation of plasmid DNA in Escherichia coli hopE (recD) mutants

The hopE mutants of Escherichia coli, which cannot stably maintain a mini-F plasmid during cell division, have mutations in the recD gene coding for subunit D of the RecBCD enzyme (exonuclease V). A large amount of linear multimer DNA of mini-F and pBR322 plasmid accumulates in these hopE mutants. The linear multimers of plasmid DNA in the hopE (recD) mutants accumulate in sbc+ genetic backgrounds and this depends on the recA+ gene function. Linear plasmid multimers also accumulated in a recBC xthA triple mutant, but not an isogenic xth A mutant or an isogenic recBC mutant. The recBC xth A mutant is defective in the conjugative type of recombination. Linear plasmid multimers were not detected in the recBC strain. We propose models to account for linear multimer formation of plasmids in various mutants.

Influenza antibody titers after vaccination of chronic renal failure patients; before and during hemodialysis, or on continuous ambulatory peritoneal dialysis

Anti-influenza antibody (Ab) titers were measured in order to elucidate whether there are any disturbances in Ab production in chronic renal failure (CRF) patients. A total of 55 CRF patients plus 15 normal individuals were vaccinated with influenza vaccine twice, 4 weeks apart of the 55 CRF patients, 15 were not on dialysis, 10 were undergoing hemodialysis (HD), and 30 were on continuous ambulatory peritoneal dialysis (CAPD). Of the 30 CAPD patients, 14 had peritonitis. Serum Ab titers were measured by complement fixation (CF) and hemagglutination inhibition (HI) tests, and IgG and IgM class specific antibodies by ELISA. All groups responded to immunization, but CAPD patients with peritonitis and CRF patients not yet on dialysis did not show a significant elevation in IgM class Ab titers. The number of CAPD patients with peritonitis who achieved positive titers was significantly lower in HI (p less than 0.01) and IgG class antibodies (p less than 0.05) compared with normal controls. Two patients with frequent peritonitis did not show any response to vaccination. It was concluded that patients with renal dysfunction have some abnormalities in Ab production against influenza vaccine, the effects of which were more pronounced in the CAPD patients with frequent peritonitis.