Nakai H, Richardson C C
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
J Biol Chem. 1988 Jul 15;263(20):9831-9.
In this paper we compare the effect of single-stranded DNA-binding proteins of bacteriophage T7 (gene 2.5 protein) and of Escherichia coli (SSB) at the T7 replication fork. The T7 gene 4 protein acts processively as helicase to promote leading strand synthesis and distributively as primase to initiate lagging strand synthesis by T7 DNA polymerase. On a nicked double-stranded template, the formation of a replication fork requires partial strand displacement so that gene 4 protein may bind to the displaced strand and unwind the helix catalytically. Both the T7 gene 2.5 protein and E. coli SSB act stoichiometrically to promote this initial strand displacement step. Once initiated, processive leading strand synthesis is not greatly stimulated by the single-stranded DNA-binding proteins. However, the T7 gene 2.5 protein, but not E. coli SSB, increases the frequency of initiation of lagging strand synthesis by greater than 10-fold. The results suggest a specific interaction of the T7 gene 2.5 protein with the T7 replication apparatus.
在本文中，我们比较了噬菌体T7的单链DNA结合蛋白（基因2.5蛋白）和大肠杆菌的单链DNA结合蛋白（SSB）对T7复制叉的影响。T7基因4蛋白作为解旋酶连续发挥作用以促进前导链合成，并作为引发酶以分散方式启动T7 DNA聚合酶的滞后链合成。在带切口的双链模板上，复制叉的形成需要部分链置换，以便基因4蛋白可以结合到置换链上并催化解开螺旋。T7基因2.5蛋白和大肠杆菌SSB均按化学计量起作用以促进这一初始链置换步骤。一旦启动，单链DNA结合蛋白不会极大地刺激连续的前导链合成。然而，T7基因2.5蛋白而非大肠杆菌SSB将滞后链合成的起始频率提高了10倍以上。结果表明T7基因2.5蛋白与T7复制装置存在特异性相互作用。
