Rabkin S D, Richardson C C
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
J Mol Biol. 1988 Dec 20;204(4):903-16. doi: 10.1016/0022-2836(88)90050-2.
Bacteriophage T7 DNA replication is initiated at a site 15% of the distance from the genetic left end of the chromosome. This primary origin contains two tandem T7 RNA polymerase promoters (phi 1.1A and phi 1.1B) followed by an A + T-rich region. When the primary origin region is deleted replication initiates at secondary origins. We have analyzed the ability of plasmids containing cloned fragments of T7 to replicate after infection of Escherichia coli with bacteriophage T7. All cloned T7 fragments that support plasmid replication contain a T7 promoter but a T7 promoter alone is not sufficient for replication. Replication of plasmids containing the primary origin is dependent on T7 DNA polymerase and gene 4 protein (helicase/primase) and a portion of the A + T-rich region. The other T7 fragments that support plasmid replication after T7 infection are promoter regions phi OR, phi 13 and phi 6.5 (secondary origins). When both the primary and secondary origins are present simultaneously on compatible plasmids, replication of each is temporally regulated. Such regulation may play a role during T7 DNA replication.
噬菌体T7 DNA复制起始于距染色体遗传左端15%距离的位点。这个主要起始位点包含两个串联的T7 RNA聚合酶启动子（φ1.1A和φ1.1B），后面跟着一个富含A+T的区域。当主要起始区域缺失时，复制在次要起始位点起始。我们分析了含有T7克隆片段的质粒在被噬菌体T7感染大肠杆菌后进行复制的能力。所有支持质粒复制的T7克隆片段都含有一个T7启动子，但仅一个T7启动子不足以进行复制。含有主要起始位点的质粒的复制依赖于T7 DNA聚合酶和基因4蛋白（解旋酶/引发酶）以及富含A+T区域的一部分。在T7感染后支持质粒复制的其他T7片段是启动子区域φOR、φ13和φ6.5（次要起始位点）。当主要和次要起始位点同时存在于相容质粒上时，每个的复制都受到时间调控。这种调控可能在T7 DNA复制过程中起作用。
