The korF region of broad-host-range plasmid RK2 encodes two polypeptides with transcriptional repressor activity

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Abstract
Broad-host-range IncP plasmid RK2 possesses a series of operons involved in plasmid maintenance, whose expression is coordinated by a number of regulators, most of which are encoded in the central regulatory korA-korB operon. The nucleotide sequence of two new cistrons in this operon, comprising what we have previously designated the korF locus located between coordinates 57.0 and 56.0 kb on the genome of the IncP alpha plasmid RK2, is presented. The cistrons encode polypeptides of 173 and 175 amino acids. Each can repress transcription from the promoters for the kfrA (a monocistronic operon which follows the korA-korB operon) and trfA (a polycistronic operon encoding a putative single-stranded-DNA-binding protein as well as the essential plasmid replication protein TrfA) operons. In addition, the korF loci allow korB to repress kfrA transcription. Both polypeptides contain hydrophobic segments, suggesting that they may be membrane associated. KorFI is highly basic protein whose predicted properties are similar to those of histone like proteins.