Morgan Elizabeth A, Shah Naseem, Symington Lorraine S
Department of Microbiology and Institute of Cancer Research, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Mol Cell Biol. 2002 Sep;22(18):6336-43. doi: 10.1128/MCB.22.18.6336-6343.2002.
Rad51 can promote extensive strand exchange in vitro in the absence of ATP hydrolysis, and the Rad51-K191R mutant protein, which can bind but poorly hydrolyze ATP, also promotes strand exchange. A haploid strain expressing the rad51-K191R allele showed an equivalent sensitivity at low doses of ionizing radiation to rad51-K191A or rad51 null mutants and was defective in spontaneous and double-strand break-induced mitotic recombination. However, the rad51-K191R/rad51-K191R diploid sporulated and the haploid spores showed high viability, indicating no apparent defect in meiotic recombination. The DNA repair defect caused by the rad51-K191R allele was suppressed in diploids and by mating-type heterozygosity in haploids. RAD54 expressed from a high-copy-number plasmid also suppressed the gamma-ray sensitivity of rad51-K191R haploids. The suppression by mating-type heterozygosity of the DNA repair defect conferred by the rad51-K191R allele could occur by elevated expression of factors that act to stabilize, or promote catalysis, by the partially functional Rad51-K191R protein.
在没有ATP水解的情况下，Rad51能在体外促进广泛的链交换，并且Rad51-K191R突变蛋白虽然能结合ATP但水解能力很差，也能促进链交换。表达rad51-K191R等位基因的单倍体菌株在低剂量电离辐射下对rad51-K191A或rad51缺失突变体表现出同等的敏感性，并且在自发和双链断裂诱导的有丝分裂重组中存在缺陷。然而，rad51-K191R/rad51-K191R二倍体能够形成孢子，并且单倍体孢子具有高活力，表明减数分裂重组没有明显缺陷。由rad51-K191R等位基因引起的DNA修复缺陷在二倍体中以及单倍体中的交配型杂合状态下受到抑制。从高拷贝数质粒表达的RAD54也抑制了rad51-K191R单倍体对γ射线的敏感性。rad51-K191R等位基因赋予的DNA修复缺陷通过交配型杂合状态的抑制可能是由于部分功能性的Rad51-K191R蛋白作用于稳定或促进催化的因子表达升高所致。
