Mutations in the trfA replication gene of the broad-host-range plasmid RK2 result in elevated plasmid copy numbers.
Mutated forms of trfA, the replication protein gene of plasmid RK2, that support a minimal RK2 origin plasmid in Escherichia coli at copy numbers up to 23-fold higher than normal have been isolated. Six such high-copy-number (copy-up) mutations were mapped and sequenced. In each case, a single base transition led to an amino acid substitution in the TrfA protein primary sequence. The six mutations affected different residues of the protein and were located within a 69-base-pair region encoding 24 amino acids. Dominance tests showed that each of the mutants can be suppressed by wild-type trfA in trans, but suppression is highly dependent on the amount of wild-type protein produced. Excess mutant TrfA protein provided in trans significantly increased the copy number of RK2 and other self-replicating derivatives of RK2 that contain a wild-type trfA gene. These observations suggest that the mutations affect a regulatory activity of the TrfA replication protein that is a key factor in the control of initiation of RK2 replication.
Center for Molecular Genetics, University of California, San Diego, La Jolla 92093.
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Durland
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Toukdarian
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Fang
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Helinski
D000483:Alleles; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000235:genetics*; D015183:Restriction Mapping
D001426:Bacterial Proteins