Novick R P, Adler G K, Projan S J, Carleton S, Highlander S K, Gruss A, Khan S A, Iordanescu S
EMBO J. 1984 Oct;3(10):2399-405. doi: 10.1002/j.1460-2075.1984.tb02146.x.
pT181 is a fully sequenced 4.4-kb 20 copy Tcr plasmid from Staphylococcus aureus. Its replication system involves a unique unidirectional origin embedded in the coding sequence for a plasmid-determined protein, RepC, that is required for initiation. When joined to a 55 copy carrier plasmid, pE194, pT181 excludes autonomous isologous replicons by inhibiting their replication. Two types of spontaneous pT181 copy mutants have been isolated, one that eliminates sensitivity to this inhibition and another that does not. A spontaneous 180-bp deletion, delta 144, eliminates both the inhibitory activity and sensitivity to it. This deletion increases copy number by 50-fold and RepC production by at least 10-fold. It is located directly upstream from the repC coding sequence and the deletion-bearing plasmid supports the replication of inhibitor-sensitive plasmids in cells containing active inhibitor. This effect is probably due to the overproduction of RepC by the delta 144 plasmid. On the basis of these results, it is suggested that RepC synthesis is negatively controlled by an inhibitor that is encoded directly upstream from the repC coding sequence and acts as a tareget set in the same region. It is likely, therefore, that pT181 replication rate is determined by the level of RepC.
pT181是一种来自金黄色葡萄球菌的、已完全测序的4.4千碱基对、含20个拷贝的Tcr质粒。其复制系统涉及一个独特的单向复制起点，该起点嵌入在一种质粒决定蛋白RepC的编码序列中，RepC是启动复制所必需的。当与一个含55个拷贝的载体质粒pE194连接时，pT181通过抑制自主同源复制子的复制来排除它们。已分离出两种类型的自发pT181拷贝突变体，一种消除了对这种抑制的敏感性，另一种则没有。一个180碱基对的自发缺失，即δ144，消除了抑制活性及其敏感性。这种缺失使拷贝数增加了50倍，RepC产量至少增加了10倍。它位于repC编码序列的直接上游，携带缺失的质粒在含有活性抑制剂的细胞中支持对抑制剂敏感的质粒的复制。这种效应可能是由于δ144质粒导致RepC过量产生。基于这些结果，有人提出RepC的合成受到一种抑制剂的负调控，该抑制剂直接编码在repC编码序列的上游，并在同一区域起靶标作用。因此，pT181的复制速率可能由RepC的水平决定。
