REGULATION OF THE F-PLASMID TRAY PROMOTER IN ESCHERICHIA-COLI BY HOST AND PLASMID FACTORS

F plasmid DNA transfer (tra) gene expression in Escherichia coli is regulated by chromosome- and F-encoded gene products. To study the relationship among these regulatory factors, we constructed low-copy plasmids containing a Φ(traY′-'lacZ)hyb gene that couples β-galactosidase and Lac permease synthesis to the F plasmid tra Y promoter. Wild-type transformants maintained high levels of β-galactosidase over a broad range of culture densities. Primer extension analysis of tra mRNA from F′lac and Φ(traY′-′lacZ)hyb strains indicated very similar, though not identical, transcription initiation sites. Moreover, Φ(tra Y′-′lacZ)hyb gene expression required both TraJ and SfrA, as does tra gene expression in F+ strains. β-Galactosidase activity was reduced ≈30-fold in the absence of TraJ, which could be supplied in cis or in trans. In a two-plasmid system in which TraJ was supplied in trans by a lac-traJ operon fusion, Φ(tra Y′-′lacZ)hyb expression was a linear, saturable function of traJ expression. Enzyme activity was reduced ≈ tenfold in sfrA mutants. That reduction could not be attributed to an effect on the TraJ level. Several other cellular or environmental variables had only a modest effect on Φ(traY′-′lacZ)hyb expression. Hyperexpression was observed at high cell density (twofold) and in anaerobic cultures (1.2-to 1.5-fold). In contrast, expression was reduced twofold in integration host factor mutants. © 1991.