| Research Abstract |
The genetic background of the control circuit in Escherichia coli that co-ordinate DNA replication and cell division of the cells was studied using the F plasmid. Two plasmid coded genes letA and letD controls the coupling between DNA replication of the F plasmid and cell division of the host bacteria (Miki, et al., J.Mol.Biol. 174 605-625 (1984); Miki, et al., ibid., 174 627-646 (1984)). The letD gene product acts to inhibit cell division of the bacteria, whereas the letA gene product acts to suppress the inhibitory activity of the letD gene product and to induce cell division. To investigate bactrial genes that participate in this coupling, we attempted to identify the target of the division inhibitor of the F plasmid. Mutants of presumptive target proteins of the letD gene product were obtained among bacterial mutants that escaped the letD product growth inhibition that occurs in hosts carrying an FletA mutant. By phage Pl mediated transduction, complementation analysis and nucleoti
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de sequencing, the mutants isolated (TDI) were classified into five groups: mutants carrying mutations in the groES (Miki, et al., J.Mol.Biol. 201 327-338 (1988)), groEL, gyrA, tdiC or tdiD genes. The gyrA gene codes for subunit a of DNA gyrase, the enzyme responsible for unlinking circular daughter chromosome after a round of replication and for maintaining the superhelical density of the bacterial chromosome. Wild type gyrA gene cloned on a high copy plasmid suppressed the growth inhibition caused by the letD gene product, suggesting that overproduction of the gyrA gene product overcomes the inhibitory activity of the letD gene product. The letD gene product presumaly acts directly on dna gyrase and, as a result, inhibits segregation of the chromosome and cell division of the host bacteria. The groES and groEL gene products supposedly participate in these processes as molecular chaperones. The tdiC and tdiD are novel genes and analyses of their structure and function are now under way. Less
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