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M Morimyo

Publications and source records attributed to M Morimyo.

29 records · Page 2Linked to original sources
PubMed1988

Isolation and characterization of methyl viologen-sensitive mutants of Escherichia coli K-12.

Escherichia coli mutants sensitive to methyl viologen (MV), an active oxygen propagator, were isolated. Among them, the new genes mvrA and mvrB were mapped at 7 and 28 min on the E. coli linkage map, respectively. MV toxicity was exerted only in the presence of oxygen and was suppressed by the radical scavenger uric acid but not by the hydroxyl radical scavenger mannitol. The mvr mutants were sensitive only to MV and had a normal repair capacity for the MV-damaged DNA. From these results, these mutants were assumed to be related to the elimination of MV-specific toxic species. Gene mvrA was cloned into vector pBR322 and its sequence was determined. The mvrA gene, which was predicted to range in size from 600 to 900 base pairs (bp) by transposon Tn1000 insertion analysis, was identified to be 807 bp, with an approximately 60-bp promoter sequence carrying consensus sequences for the -35 region, the -10 region, and a ribosome-binding site. The MvrA protein deduced from the DNA sequence was 29.7 kilodaltons, which was in good agreement with the 29 kilodaltons of the MvrA protein identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after a maxicell labeling experiment.

Amino Acid Sequence↗
PubMed1982

Anaerobic incubation enhances the colony formation of a polA recB strain of Escherichia coli K-12.

Escherichia coli strain E247 (polA1 recB21) has reduced colony formation (even at the permissive temperature of 30 degrees C) because of a poor suppressor mutation (sup-126). The colony formation was enhanced in the absence of oxygen about 3-fold at 30 degrees C and 10(6)-fold at 43 degrees C, suggesting that a polA recB strain was inviable due to oxygen toxicity. Colony formation was also increased by incubation in an agar medium containing the reducing agent thioglycolate and incubation in the presence of chloroform-killed Saccharomyces cerevisiae pet+ cells, but not pet cells. Since the E247 strain viability was inversely dependent on the oxygen pressure and since the strain was more sensitive to superoxide radical than either the polA or the recB mutant, it seems likely that the polA and recB genes play a role in repairing DNA damage during respiration.

Anaerobiosis↗
PubMed1976

Evidence that the gene uvrB is indispensable for a polymerase I deficient strain of Escherichia coli K-12.

Conclusive evidence in presented to show that the gene uvrA is dispensable, but the uvrB is indispensable for an Escherichia coli strain carrying gene polA1. We constructed strains E139 (sup-126 polAl uvrB59) and E159 (sup-126 polAl uvrA43) where mutations polAl, uvrB59 and uvrA43 are amber mutations and mutation sup-126 is an amber suppressor mutation effective at 30 degrees C but not at 42 degrees C. At 42 degrees C, strain E139 is inviable but strain E159 viable whereas both are viable at 30 degrees C. Revertants of E139 viable at 42 degrees C occurred spontaneously at a frequency of about 3 X 10(-4). One of the revertants was shown to be caused by suppressor mutation, designated spu, rather than back mutation of the gene uvrB59 or polAl or amber suppressor mutation. Viabilities of the revertants varied from 10(-3) to 1.0 at 42 degrees C compared with those of 30 degrees C. At 42 degrees C, all the revertants with normal viabilities at 42 degrees C were non-filamentous in contrast to the filamentous character of E139. However, strain E159 was viable at 42 degrees C despite its filamentous character. We conclude that the gene uvrB is involved not only in excision repair but also in normal growth in a polA background.

DNA Repair↗
PubMed1975

A mutant of Eshcerchia coli K-12, URT-43, with a temperature-sensitive defect at the incision step of the excision repair mechanism.

URT-43, which has a defect in excision repair, exhibits a temperature-dependent ultraviolet survival. It was shown that URT-43 requires protein synthesis but not DNA synthesis for recovery, by examining recovery in a growth medium containing chloramphenicol or nalidixic acid. The recovery of irradiated bacteriophage lambda in URT-43 took place in a medium containing nalidixic acid at 30 degrees, but not at 41 degrees, and chloramphenicol prevented this recovery. These results seem to imply that the product of the mutated gene in URT-43 is labile. URT-43 was confirmed to have a temperature-sensitive mutation at the incision step of the excision repair mechanism by examining the nick formation of parental DNA in alkaline sucrose gradients. The release of pyrimidine dimers was reinvestigated directly by one- and two-dimensional paper-chromatography and indirectly by examining the distribution of DNA molecules synthesized after irradiation. Dimers were excised into the acid-soluble fraction when growing bacteria were incubated, but were not excised when in amino acid starved bacteria. These results suggest that URT-43 is a mutant slowly excising pyrimidine dimers because the product of a mutated gene concerned with the incision step of the excision repair mechanism is unstable.

Centrifugation, Zonal↗
PubMed1971

Temperature-sensitive recovery of a mutant of Escherichia coli K-12 irradiated with ultraviolet light.

URT-43 is a mutant of Escherichia coli K-12 which gives a much larger number of survivors when ultraviolet (UV)-irradiated bacteria are incubated on agar medium at 30 C than when they are incubated on the medium at 41 C, although in both cases the number of survivors is fewer than that given by its wild-type ancestor. The UV sensitivity of this mutant was found to be markedly influenced by the presence of a high concentration of NaCl or sucrose in the plating medium. Thus, when irradiated bacteria were plated on agar medium containing 2% NaCl or 0.5 m sucrose at 30 C, they exhibited a resistance similar to that of their wild-type ancestor. At 30 C, there was also an extensive recovery in liquid M9 medium supplemented with all of the nutrients required for growth and NaCl or sucrose. At 41 C, however, the recovery was greatly inhibited. Direct chemical analysis of thymine dimers has revealed that no significant amount of the dimer was released from deoxyribonucleic acid during the period of extensive recovery. It was concluded, therefore, that the temperature-sensitive recovery of URT-43 does not accompany excision of the bulk of pyrimidine dimers. To learn the gene function involved in the recovery, double mutants carrying an additional mutation either in a uvr or a rec gene have been investigated for their UV sensitivities and recovery in liquid medium. It was found that recA(-) and recB(-) derivatives retain the ability of undergoing an efficient recovery at a low temperature, whereas uvrB(-) and uvrC(-) derivatives have completely lost this ability. For these reasons, it was concluded that the mechanism responsible for the recovery of URT-43 involves the function controlled by the uvr genes. The results of photoreactivation suggested that most of the entities dealt with during recovery were pyrimidine dimers.

Agar↗