H-NS and Lrp serve as positive modulators of traJ expression from the Escherichia coli plasmid pRK100.

Conjugative transfer of F-like plasmids is a tightly regulated process. The TraJ protein is the main positive activator of the tra operon which encodes products required for conjugative transfer of F-like plasmids. Nucleotide sequence analysis revealed potential Lrp and H-NS binding sites in the traJ regulatory region. Expression of a traJ-lacZ fusion in hns and lrp mutant strains showed that both are positive modulators of traJ expression. Competitive RT-PCR demonstrated that H-NS and Lrp exert their effect at the transcriptional level. Electrophoretic mobility-shift assays showed that H-NS and Lrp proteins bind to the traJ promoter. Conjugative transfer of pRK100 was decreased in hns but not in lrp mutant strains. Together, the results indicate H-NS and Lrp function as activators of traJ transcription.