Belokrysenko S S
Genetika. 1978;14(1):145-53.
Escherichia coli CTR1(RT1)RHfm1) carrying two H-factors and having unusually high frequency of mutation to high level streptomycin resistance is studied. The high frequency of mutation (about 10(-6) to streptomycin resistance is connected with the presence of R factor RHfm1, controlling the resistance to chloramphenicol and low level streptomacin resistance, but not with RT1, controlling the resistance to tetracycline. Spontaneous or ethidium bromide-induced loss of RHfm1 is accompanied by a decrease of the mutation frequency to 10(-9). RHfm1 is efficiently transmissible to other strains at 28 degrees C. The acquisition of RHfm1 by strains of E. coli K-12 ans S. typhimurium LT2 was followed by a 1000--10000-fold increase of the frequejcy of mutation to streptomycin resistance. Some streptomycin resistant mutants were isolated, and chromosome location of the mutations was demonstrated. The streptomycin resistant mutants were unable to transmit high level of resistance to streptomycin with R factor, but only low level one. The loss of RHfm1 by streptomycin resistant mutants was accompanied by the return to the streptomycin sensitivity of the initial R- strans (E. coli K-12 mutants) or by a decrease of the streptomycin resistance to the level, only 2-fold higher than that of R- wild type (E. coli CTR1 mutant). Thus, the mutantions had practically no effect on streptomycin resistance of R- strains, but could lead to high resistance phenotypes in the presence of RHfm1. The mutant loci in all three studied strains were found to be closely linked to the locus "fus" on the genetic map of E. coli.
对携带两种H因子且对高浓度链霉素耐药突变频率异常高的大肠杆菌CTR1（RT1）RHfm1进行了研究。高突变频率（约10^(-6)）与链霉素耐药性相关，这与R因子RHfm1的存在有关，RHfm1控制对氯霉素和低水平链霉素的耐药性，但与控制对四环素耐药性的RT1无关。RHfm1的自发或溴化乙锭诱导丢失伴随着突变频率降至10^(-9)。RHfm1在28℃时能有效地转移到其他菌株。大肠杆菌K - 12和鼠伤寒沙门氏菌LT2菌株获得RHfm1后，对链霉素耐药的突变频率增加了1000 - 10000倍。分离出了一些链霉素耐药突变体，并证明了突变的染色体定位。链霉素耐药突变体无法通过R因子传递高水平的链霉素耐药性，而只能传递低水平的耐药性。链霉素耐药突变体丢失RHfm1后，初始R - 菌株（大肠杆菌K - 12突变体）恢复对链霉素的敏感性，或者链霉素耐药性降至仅比R - 野生型（大肠杆菌CTR1突变体）高2倍的水平。因此，这些突变实际上对R - 菌株的链霉素耐药性没有影响，但在存在RHfm1时可导致高耐药表型。在所有三个研究菌株中发现的突变位点与大肠杆菌遗传图谱上的“fus”位点紧密连锁。
