Ziegelin G, Lanka E
Max-Planck-Institut für Molekulare Genetik, Abteilung Schuster, Berlin, Germany.
FEMS Microbiol Rev. 1995 Aug;17(1-2):99-107. doi: 10.1111/j.1574-6976.1995.tb00191.x.
Replication of satellite phage P4 of Escherichia coli is dependent on three phage-encoded elements: the origin (ori), a cis replication element (crr), and the product of the alpha gene, gp alpha. In P4 replication is origin-specific resulting in monomeric form I DNA. DNA synthesis requires chromosomally encoded proteins DNA polymerase III holoenzyme, SSB, DNA gyrase and probably topoisomerase I; host-encoded initiation and priming functions are dispensable. The alpha protein is multifunctional in P4 replication, combining three activities in a single polypeptide chain. First, the protein complexes specifically with type I repeats at ori and crr. Second, the helicase activity associated with gp alpha unwinds DNA with 3'--> 5' polarity. Third, the primase activity results in the synthesis of RNA primers. Defined sequence motifs in gp alpha correlate with the helicase and primase activities which are arranged in distinct, separable domains. Primase activity is associated with the N-terminal half of the protein, ori/crr binding with the C-terminal portion. A model for the initiation mechanism of P4 replication which resembles that of mammalian simian virus 40 is discussed.
大肠杆菌卫星噬菌体P4的复制依赖于三种噬菌体编码元件：复制起点（ori）、顺式复制元件（crr）和α基因的产物gpα。在P4中，复制是起点特异性的，产生单体形式I的DNA。DNA合成需要染色体编码的蛋白质DNA聚合酶III全酶、单链结合蛋白（SSB）、DNA促旋酶以及可能的拓扑异构酶I；宿主编码的起始和引发功能是不必要的。α蛋白在P4复制中具有多种功能，在单一多肽链中兼具三种活性。首先，该蛋白与ori和crr处的I型重复序列特异性结合。其次，与gpα相关的解旋酶活性以3'→5'极性解开DNA。第三，引发酶活性导致RNA引物的合成。gpα中特定的序列基序与解旋酶和引发酶活性相关，这些活性分布在不同的、可分离的结构域中。引发酶活性与该蛋白的N端一半相关，ori/crr结合与C端部分相关。本文讨论了一种类似于哺乳动物猿猴病毒40的P4复制起始机制模型。
