|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1994 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1993 : ¥1,300,000 (Direct Cost : ¥1,300,000)
The letA (ccdA) and letD (ccdB) genes of the F plasmid, located just outside the sequence essential for replication, contribute to stable maintenance of the plasmid in Escherichia coli cells. The letD gene product acts to inhibit partitioning of chromosomal DNA and cell division by inactivating the A subunit of DNA gyrase by a direct interaction, whereas the letA gene product acts to reverse the inhibitory activity of the letD gene product. To identify the host factor (s) involved in this process, we analyzed such mutants that escaped the letD product growth inhibition and their suppressor, and found that three E.coli genes, tldD,tldE and zfiA participate, in addition to the groE genes we reported previously. tldD and tldE mutations made cells tolerant to the letD product growth inhibition as did groES mutations, while the mutation in the zfiA gene made tldD,tldE and groES mutants letD sensitive. We assume that these gene products are factors that modulate activity of DNA gyrase along with the letD gene product ; zfiA gene product acts to inhibit interaction between the letD protein and the A subunit of DNA gyrase, while the tldD,tldE and zfiA gene products act to suppress the inhibitory activity of the zfiA gene product. The tldD,tldE and zfiA genes are located at 70.4,96.0 and 58.2 minutes on the E coli chromosome, respectively, and code for proteins with relative molecular masses of 51,000,48,000 and 6800, respectively. The tldD is a novel gene, but the tldE and zfiA genes proved to be the pmbA gene (production of Microcin B17) and the csrA gene (carbon strage regulator), respectively.