Dai D X, Ishiguro E E
Department of Biochemistry and Microbiology, University of Victoria, B.C., Canada.
Can J Microbiol. 1991 Feb;37(2):122-7. doi: 10.1139/m91-018.
The murH mutant of Escherichia coli exhibits temperature-sensitive growth and lysis at the restrictive temperature. Temperature-resistant derivatives of the mutant occurred at a frequency of about 3 X 10(-6). All of the seven independent isolates examined were shown to be pseudorevertants carrying extragenic suppressors of murH, which mapped at 24.5 min on the linkage map. One allele, apparently representing a new locus, designated smhA, was characterized further. The smhA mutation by itself conferred no recognizable phenotype. However, smhA suppressed the temperature-sensitive lysis phenotype of the murH mutant. The smhA mutant acquired a spontaneous mutation in another new gene, designated lytE, which was mapped at 25 min. The lytE mutation by itself conferred a temperature-sensitive lysis phenotype indistinguishable from that of the murH mutant. The lytE mutation was suppressed by smhA as well as by another suppressor of murH designated smhB. The suppressor activity of smhA was apparently relatively specific in that smhA failed to prevent lysis caused by either mutational or antibiotic-induced blocks in peptidoglycan synthesis. The possibility that the smhA and lytE genes are functionally related to murH is considered.
大肠杆菌的murH突变体在限制温度下表现出温度敏感型生长和裂解。该突变体的温度抗性衍生物出现的频率约为3×10⁻⁶。所检测的七个独立分离株均显示为携带murH基因外抑制子的假回复体，这些抑制子在连锁图谱上位于24.5分钟处。对一个等位基因进行了进一步表征，该等位基因显然代表一个新位点，命名为smhA。smhA突变本身并未赋予可识别的表型。然而，smhA抑制了murH突变体的温度敏感型裂解表型。smhA突变体在另一个名为lytE的新基因中获得了一个自发突变，该基因位于25分钟处。lytE突变本身赋予了一种与murH突变体无法区分的温度敏感型裂解表型。lytE突变被smhA以及murH的另一个抑制子smhB所抑制。smhA的抑制活性显然相对特异，因为smhA无法阻止由肽聚糖合成中的突变或抗生素诱导的阻断所导致的裂解。人们考虑了smhA和lytE基因在功能上与murH相关的可能性。
