Genetic structure and stability of a copy number mutant of IncFI group plasmid ColV-K94 in Escherichia coli K-12

Cloning and DNA sequence of plasmid determinant iss, coding for increased serum survival and surface exclusion, which has homology with lambda DNA

Escherichia coli K12 cells carrying a cloned 1.4 kb HindIII fragment from plasmid ColV2-K94, showed increased survival in guinea pig serum. The recombinant plasmid also conferred group II surface exclusion, i.e. the cells were reduced in recipient ability towards the incoming plasmid R538drd in conjugation experiments. Southern blotting suggested homology with bacteriophage lambda DNA and to the insertion element IS2. Determination of the DNA sequence of the fragment demonstrated the presence of a truncated IS2 (165 bp), separated by 250 bp from a 900 bp stretch of homology with lambda DNA, beginning within the Rz gene and continuing in the rightward direction on the lambda map. A 97 amino acid open reading frame (ORF) adjacent to Rz and on the opposite strand, remained intact in iss, with several amino acid changes. The ORF in iss is preceded by sequences resembling prokaryotic ribosome binding sites and promoters.

finO sequences on conjugally repressed and derepressed F-like plasmids

DNA-DNA hybridization studies have demonstrated the physical relatedness of the fertility inhibition gene, finO, among both FinO+ and FinO- F-like conjugative plasmids, viz. ColV2-K94, R100-1,R1drd19,R1,R6-5, UCR123, R386, p307, R453, R773, and pIP162-1. Furthermore, the data indicate that finO sequences on the FinO- plasmid ColV2-K94 map downstream of the transfer region, within 93.6-95.3 ColV2-K94.

Incompatibility repressor in a RepA-like replicon of the IncFI plasmid ColV2-K94

The replication region Rep1 of the IncFI plasmid ColV2-K94 was cloned on self-replicating restriction fragments. Rep1 was structurally and functionally homologous to the RepA replicon of IncFII R plasmids. Despite this close relationship, these two replication systems were compatible with each other. The nucleotide sequence of the copA incompatibility-replication control gene of Rep1 was determined and compared with the copA sequence of RepA. Six base changes were found in a 24-base-pair span of the copA gene; these may result in the formation of a new, more stable, 49-base stem-loop structure in the potential CopA RNA repressor molecule. We postulate that these alterations weaken the interaction between RNA transcripts of the Rep1 and RepA replicons.

A physical and genetic map of the IncFI plasmid ColV2-K94

A restriction enzyme map of the IncFI plasmid ColV2-K94 was generated using EcoRI, BamHI, HindIII, and XhoI; the genetic features of this element were then mapped from previous heteroduplex studies.

Second replicon in ColV2-K94 mediates the stable coexistence of two incompatible plasmids

The colicin-producing plasmid pWS12, a Tn903 derivative of ColV2-K94, was found to be incompatible with the IncFI plasmids KLF1 and R386. It was compatible with the IncFII plasmids R538 and R100. Three overlapping mini-ColV derivatives, pWS15, pWS16 and pWS17, were obtained by restriction digestion of pWS12. Unlike pWS12, pWS16 exhibited incompatibility with both IncFI and IncFII plasmids, whereas the pWS15 and pWS17 plasmids expressed IncFII incompatibility but not the IncFI incompatibility of their parental ColV plasmid. We show that, although pWS12 has an IncFII replicon, Rep1, it does not normally express IncFII incompatibility because a second replicon, Rep2 (homologous to the secondary replicon of F), functions during the stable coexistence of the plasmid with IncFII plasmids. When Rep2 is deleted (as in the mini-ColV plasmids) or made nonfunctional (as in a PolA mutant strain), ColV then behaves as an IncFII plasmid.