Tranlocation of Conjugative Plasmid and Prespore Chromosome across Membrane during Sporulation in Streptomyces

本文报道了产硫链丝菌素链球菌（Strep thiostrepton-producing tomorrow，S.c.）接合性质粒转移和前孢子染色体在细胞间分配过程中的事件和复制。对与质粒DNA和前孢子染色体DNA转移功能相关的基因或蛋白质，如转移基因（分别由质粒和宿主染色体编码的tra和spoIII样基因）、复制因子（ori、rep）、ssDNA结合蛋白、组蛋白样蛋白基因（hup）及其产物进行了测定。这些数据和观察表明如下。质粒和前孢子染色体DNA的易位可以通过在ori处引入切口形成ssDNA来触发，ssDNA转移的能量来源于具有ATP结合位点的Tra和SpoIII样跨膜蛋白上的ATP水解。hup基因产物对ssDNA的包被也可能发生在易位过程中和受体细胞中。虽然SpoIIIE样蛋白对于链霉菌细胞中的孢子形成是必要的，但是由于两个基因的结构和功能相似性，Tra蛋白似乎通过竞争抑制它们的孢子形成。spoIIIE样基因在后分隔染色体分配中也起重要作用。质粒转移被肽类抗生素杆菌肽抑制。分离到两个由杆菌肽诱导的膜蛋白（32和38 kDa），前者未知，后者为ABC转运蛋白。这些蛋白质可能参与了质粒转移和前孢子染色体分配之间的竞争，同时，我们还确定了接合线性质粒的特性，它抑制了接合环状质粒的有害作用（抑制孢子形成和硫链丝菌素生产）。

This report concerns events and replication during the conjugative plasmid trasnfer and prespore chromosome partitioning between the cells in thiostrepton-producing Strep tomyces, S.c. azureus and S.Iaurentii.We determined the genes or proteins functionaly related to the transfer of plasmid DNA and prespore chromosome DNA, such as trasfer genes (tra and spoIIIE-like gene encoded by plasmid and host chromosome, respectively), replication factors (ori, rep) , and ssDNA-binding protein, histone-like protein gene (hup), and their products. These data and observation suggested as follows. Translocation of plasmid and prespore chromosome DNA may be triggered by introduction of a nick at ori to form ssDNA.The energy of ssDNA transfer would derive from by the hydrolysis of ATP on the Tra and SpoIIIE-like transmenbrane proteins, which have an ATP binding site. Coating of ssDNA by hup gene product may also occur during the translocation and in the recipient cell. Although the SpoIIIE-like protein would ben ecessary for sporulation in Streptomyces cells, Tra protein seems to inhibit their sporulation by a competition, owing to structural and functional similarities of both genes. It is also suggested that spoIIIE-like gene is also important in postseptational chromosome partitioning. The plasmid transfer was inhibited by a peptide antibiotic bacitracim. On the contrary, the prespore partitioning was stimulated by it. Two bacitracin-induced menbrane proteins (32 and 38 kDa) were isolated : the former was unknown, but the latter was ABC-transporter. These proteins may participate in the competition between plasmid transfer and prespore chromosome partitioning.On the other hand, we also determined the characteristics of a conjugative linear plasmid, which suppressed the injurious effects (inhibition of sporulation and thiostrepton productivity) of conjugative circular plasmid.