Gielow A, Diederich L, Messer W
Max-Planck-Institut fur Molekulare Genetik, Berlin, Federal Republic of Germany.
J Bacteriol. 1991 Jan;173(1):73-9. doi: 10.1128/jb.173.1.73-79.1991.
The phage-plasmid hybrid phasyl can replicate as a phage in the presence of a filamentous phage of Escherichia coli (M13, fl, fd). The extragenic region of phasyl shows homology with the plus and the minus origins of filamentous phages. Insertion of a Cmr fragment into the plus origin or of a Kmr fragment into the minus origin resulted in a reduced transduction frequency, while insertion into other parts of the extragenic region did not. This suggests that phagelike replication of phasyl is mediated by an origin that coincides with the two homologous elements in the extragenic region. Autonomous replication of phasyl occurs from a second origin (oriA) that is located between positions 297 and 636. This fragment mediates replication if the Arp protein is supplied in trans. Arp is the only phage-encoded protein and is essential for plasmidlike replication. No sequence homology to other known origins was found. Phasyl derivatives with either one of the two origins inactivated can be rescued via the alternative replication mode, suggesting that the two replication pathways are independent.
噬菌体 - 质粒杂种phasyl在存在大肠杆菌丝状噬菌体（M13、fl、fd）的情况下可作为噬菌体进行复制。phasyl的基因外区域与丝状噬菌体的正链和负链起始位点具有同源性。将Cmr片段插入正链起始位点或Kmr片段插入负链起始位点会导致转导频率降低，而插入基因外区域的其他部分则不会。这表明phasyl的噬菌体型复制是由一个与基因外区域中的两个同源元件重合的起始位点介导的。phasyl的自主复制发生在位于297和636位之间的第二个起始位点（oriA）。如果反式提供Arp蛋白，该片段可介导复制。Arp是唯一由噬菌体编码的蛋白质，对质粒样复制至关重要。未发现与其他已知起始位点的序列同源性。两个起始位点之一失活的phasyl衍生物可通过替代复制模式挽救，这表明两种复制途径是独立的。
