Sigal N, Delius H, Kornberg T, Gefter M L, Alberts B
Proc Natl Acad Sci U S A. 1972 Dec;69(12):3537-41. doi: 10.1073/pnas.69.12.3537.
A DNA-unwinding protein has been purified to homogeneity from E. coli. This protein has a molecular weight of about 22,000, as judged by its electrophoretic mobility on polyacrylamide gels containing sodium dodecylsulfate, and it appears to be present in about 800 copies per log-phase cell. It binds tightly and cooperatively to single-stranded DNA, and much less tightly, if at all, to RNA or double-stranded DNA. Like the T4 gene-32 protein characterized previously, the E. coli DNA-unwinding protein depresses the melting temperature of double-stranded DNAs, with regions rich in A-T base-pairs being preferentially melted. The E. coli protein strongly stimulates in vitro DNA synthesis by E. coli DNA polymerase II on appropriate templates; however, no stimulation is found with purified polymerases I or III of E. coli, or with T4 DNA polymerase. In contrast, gene-32 protein stimulates only the T4 DNA polymerase in a parallel assay.
一种DNA解旋蛋白已从大肠杆菌中纯化至同质状态。通过其在含十二烷基硫酸钠的聚丙烯酰胺凝胶上的电泳迁移率判断，该蛋白分子量约为22,000，且在对数期细胞中似乎每细胞约有800个拷贝。它与单链DNA紧密且协同结合，而与RNA或双链DNA的结合则非常弱，甚至不结合。与先前表征的T4基因32蛋白一样，大肠杆菌DNA解旋蛋白会降低双链DNA的解链温度，富含A - T碱基对的区域会优先解链。大肠杆菌蛋白能在合适模板上强烈刺激大肠杆菌DNA聚合酶II的体外DNA合成；然而，未发现对大肠杆菌纯化的聚合酶I或III以及T4 DNA聚合酶有刺激作用。相比之下，在平行试验中，基因32蛋白仅刺激T4 DNA聚合酶。
