Jones A L, Barth P T, Wilkins B M
Department of Genetics, University of Leicester, UK.
Mol Microbiol. 1992 Mar;6(5):605-13. doi: 10.1111/j.1365-2958.1992.tb01507.x.
The Incl1 conjugative plasmid Collb-P9 carries a psiB gene that prevents induction of the SOS response in host bacteria. This locus is located 2.5 kb downstream of the ssb (single-stranded DNA-binding protein) gene in the leading region. This portion of Collb is strikingly similar to part of the leading region of the otherwise distinct F plasmid. Expression of psiB and ssb is increased when the host cell is exposed to an SOS-inducing treatment or the Collb transfer system is derepressed. Moreover, expression of both genes on a derepressed plasmid is strongly enhanced in conjugatively infected recipient cells. Carriage of the psiB gene by Collb is shown to prevent a low level of SOS induction following conjugation. Plasmid ssb and psiB genes may function to promote installation of the replicon in the new cell.
IncI1接合质粒Collb-P9携带一个psiB基因，该基因可阻止宿主细菌中SOS反应的诱导。该位点位于前导区单链DNA结合蛋白（ssb）基因下游2.5 kb处。Collb的这一部分与其他不同的F质粒前导区的一部分惊人地相似。当宿主细胞接受SOS诱导处理或Collb转移系统去阻遏时，psiB和ssb的表达会增加。此外，在接合感染的受体细胞中，去阻遏质粒上这两个基因的表达会显著增强。研究表明，Collb携带psiB基因可防止接合后出现低水平的SOS诱导。质粒ssb和psiB基因可能起到促进复制子在新细胞中建立的作用。
