Masai H, Nomura N, Arai K
Department of Molecular Biology, DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, California 94304.
J Biol Chem. 1990 Sep 5;265(25):15134-44.
A priming mechanism requiring dnaA, dnaB, and dnaC proteins operates on a single-stranded DNA coated with single-stranded DNA-binding protein. This novel priming, referred to as "ABC-priming," requires a specific hairpin structure whose stem carries a dnaA protein recognition sequence (dnaA box). In conjunction with primase and DNA polymerase III holoenzyme, ABC-priming can efficiently convert single-stranded DNA into the duplex replicative form. dnaA protein specifically recognizes and binds the single-stranded hairpin and permits the loading of dnaB protein to form a prepriming protein complex containing dnaA and dnaB proteins which can be physically isolated. ABC-priming can replace phi X174 type priming on the lagging strand template of pBR322 in vitro, suggesting a possible function of ABC-priming for the lagging strand synthesis and duplex unwinding. Similar to the phi X174 type priming, a mobile nature of ABC-priming was indicated by helicase activity in the presence of ATP of a prepriming protein complex formed at the hairpin. The implications of this novel priming in initiation of replication at the chromosomal origin, oriC, and in its contribution to the replication fork are discussed.
一种需要dnaA、dnaB和dnaC蛋白的引发机制作用于被单链DNA结合蛋白包被的单链DNA上。这种新的引发作用，被称为“ABC引发”，需要一种特定的发夹结构，其茎部携带一个dnaA蛋白识别序列（dnaA框）。与引发酶和DNA聚合酶III全酶一起，ABC引发能够有效地将单链DNA转化为双链复制形式。dnaA蛋白特异性识别并结合单链发夹，允许dnaB蛋白加载，形成一个包含dnaA和dnaB蛋白的预引发蛋白复合物，该复合物可以被物理分离。ABC引发在体外可以替代pBR322滞后链模板上的φX174型引发，这表明ABC引发在滞后链合成和双链解旋中可能具有功能。与φX174型引发类似，在发夹处形成的预引发蛋白复合物在ATP存在下的解旋酶活性表明ABC引发具有移动性。本文讨论了这种新的引发作用在染色体复制起点oriC处的复制起始及其对复制叉的贡献中的意义。
