Molecular analysis and nucleotide sequence of finQ, a transcriptional inhibitor of the F plasmid transfer genes.

We report the cloning of finQ, a gene coding for fertility inhibition of the F plasmid, from the IncI R factor R820a. The finQ gene was mapped precisely within a 1.24 kb region by ptac-transposase + min-kan mutagenesis and its product, FinQp, identified as a single polypeptide by means of SDS-polyacrylamide gel electrophoresis. Nucleotide sequencing of the finQ region allowed elucidation of the FinQp amino acid sequence and determination of its precise molecular weight as 39,895 Da. Analysis of the predicted amino acid sequence indicated that FinQp is a positively charged protein possessing a helix-turn-helix DNA binding motif. We propose a possible model for the mechanism by which FinQp terminates transcription within the F plasmid tra region. DNA-DNA hybridization established that all FinQ+ R factors examined have an homologous finQ gene.