MECHANISMS OF MUTATION IN BACTERIOPHAGE T4

在大肠杆菌中生长的噬菌体T4是一个祖先模型系统 用于研究突变和DNA修复 最近的工作产生了 以下结果。(1)热产生G：C -> T：A颠换， 非复制型T4 DNA中G残基的修饰。该过程 高度可变，似乎取决于介质的痕量组分， 可能涉及自发活化的氧物质。(2)自发 T4 rII系统中的突变率在很大程度上独立于这两个因素， 温度和介质。(3)在pH 9下生长或cya或crp突变 基因强烈地增加了E.而T_4细胞则无。的 光复活和切除修复系统在E.大肠杆菌，但不是 在T4。然而，复制修复缺陷的T4突变体似乎是 对光复活反应不敏感。(4)T4系统中的正向突变 通常通过计算出现在5个基因上的r突变体来评分。 两 其中，rI和rV仍未得到表征。 RV基因已经被定位 正在进行测序(5)噬菌体RB 69是T4的远亲。的 RB 69 DNA聚合酶与T4 DNA的氨基酸同源性仅为61.5 但是RB 69基因可以补充T4基因中的缺陷。的 这种构型中DNA复制的保真度接近正常， vivo.

Bacteriophage T4 growing in Escherichia coli is an ancestral model system for studying mutagenesis and DNA repair. Recent work has produced the following results. (1) Heat produces G:C -> T:A transversions via modification of G residues in nonreplicating T4 DNA. The process is highly variable, appears to depend on trace components of the medium, and may involve a spontaneously activated oxygen species. (2) Spontaneous mutation rates in the T4 rII system are largely independent of both temperature and medium. (3) Growth at pH 9 or mutations in the cya or crp genes strongly increases resistance to UV in E. coli, but not in T4. The photoreactivation and excision-repair systems interact in E. coli but not in T4. However, a T4 mutant defective in replication repair appers to be refractory to photoreactivation. (4) Forward mutation in the T4 system is usually scored by counting r mutants, which arise at five genes. Two of these, rI and rV, remain uncharacterized. The rV gene has been mapped and is being sequenced. (5) Phage RB69 is a distant relative of T4. The RB69 DNA polymerase shares only 61.5% amino acid identify with the T4 DNA polymerase but the RB69 gene can complement a defect in the T4 gene. The fidelity of DNA replication in this configuration is close to normal in vivo.