Tsuchimoto S, Ohtsubo H, Ohtsubo E
Institute of Applied Microbiology, University of Tokyo, Japan.
J Bacteriol. 1988 Apr;170(4):1461-6. doi: 10.1128/jb.170.4.1461-1466.1988.
Plasmid R100 was found to have two genes, designated pemK and pemI, that were responsible for its stable inheritance during cell division. They are located near the region that is essential for autonomous replication. Under conditions that inhibit replication of R100 derivatives, the plasmid containing these pem genes gave only a few segregants in viable cells and increased the number of nonviable cells in the population, suggesting that a product from the pem region stabilized the plasmid by killing plasmid-free segregants. Inactivation of one of the two translational open reading frames in the pem region caused the loss of the killing function, and thus, the open reading frame is a gene designated pemK, which encodes the killing factor. The coexistence of the pem+ plasmid with a high-copy-number plasmid carrying the other open reading frame inhibited stabilization, and thus, the second open reading frame is a gene designated pemI, which encodes the inhibitor which might control the killing function of pemK. It is likely that the two open reading frames were transcribed from a promoter. There were no significant homologies in DNA sequences between the pem gene of R100 and the genes previously shown to be responsible for the stable inheritance of the other plasmids.
发现质粒R100有两个基因，命名为pemK和pemI，它们负责其在细胞分裂过程中的稳定遗传。它们位于自主复制所必需的区域附近。在抑制R100衍生物复制的条件下，含有这些pem基因的质粒在活细胞中仅产生少数分离体，并增加了群体中非活细胞的数量，这表明pem区域的一种产物通过杀死无质粒的分离体来稳定质粒。pem区域中两个翻译开放阅读框之一的失活导致杀伤功能丧失，因此，该开放阅读框是一个名为pemK的基因，它编码杀伤因子。pem+质粒与携带另一个开放阅读框的高拷贝数质粒共存会抑制稳定性，因此，第二个开放阅读框是一个名为pemI的基因，它编码可能控制pemK杀伤功能的抑制剂。这两个开放阅读框很可能是从一个启动子转录而来的。R100的pem基因与先前显示负责其他质粒稳定遗传的基因之间的DNA序列没有明显的同源性。
