title: Host-dependent, thermosensitive replication of an R plasmid, pJY5, isolated from Enterobacter cloacae.
abstract: The thermosensitive replication of an R plasmid, pJY5, isolated from Enterobacter cloacae, was studied. pJY5 consisted of 61 million daltons of covalently closed circular (CCC) deoxyribonucleic acid (DNA) with a buoyant density of 1.714 g/cm3 (55 mol % guanine plus cytosine). In Escherichia coli, this plasmid replicated stringently at 32 degrees C, but ceased its CCC DNA replication after a short incubation at 42 degrees C, resulting in production of R- segregants. The thermosensitive replication of pJY5 was not overcome by the coexistence of non-thermosensitive R plasmids. The plasmid manifested an inhibitory effect on host bacterial cell growth at 42 degrees C, although the effect was less prominent than that of R plasmids belonging to the T-incompatibility group, Rts1, R401, and R402. When the pJY5 plasmid was transferred into E. cloacae, however, no R- segregants were detected at any culture temperature, even 42 degrees C. Alkaline sucrose gradient analysis revealed that a significant amount of pJY5 CCC DNA was synthesized in E. cloacae at the high temperature but not in E. coli. Furthermore, the growth-inhibitory effect of pJY5 on hosts at 42 degrees C was not observed in E. cloacae. On the other hand, Rts1 and R401 were found to be thermosensitive in E. cloacae as well as in E. coli.
mesh_terms: D004269:DNA, Bacterial / Q000032:analysis / Q000096:biosynthesis*; D004270:DNA, Circular / Q000032:analysis / Q000096:biosynthesis*; D004754:Enterobacter / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D004755:Enterobacteriaceae / Q000235:genetics*; D008970:Molecular Weight; D011815:R Factors; D013696:Temperature
chemical_list: D004269:DNA, Bacterial; D004270:DNA, Circular