Replication regulation of ColE1-like plasmids in amino acid-starved Escherichia coli.

Differential replication of various ColE1-type plasmids in stringent (relA+) and relaxed (relA-) strains of Escherichia coli starved for particular amino acids was reported previously. A role for the plasmid-encoded Rom protein in the stringent control of ColE1 replication has also been demonstrated. Here we have studied the efficiency of replication of five ColE1-type plasmids in E. coli relA+ and relA- strains starved for five amino acids to find the differential replication of each plasmid in cells starved for each amino acid. The efficiency of replication was found to be in positive correlation with the homology between nucleotide sequences of particular loops of RNA I or RNA II and anticodon loops of tRNA molecules corresponding to the kind of the amino acid deprived. Efficient plasmid DNA replication was observed under conditions for which we predicted (on the basis of theoretical calculations) relatively strong interactions between tRNA molecules, expected to occur in high concentrations in an uncharged from, and RNA I or RNA II. When the theoretical possibility of the tRNA-RNA I or tRNA-RNA II interactions was very small, the observed plasmid DNA replication was negligible. Replication of ColE1-like plasmids during the stringent response was observed only in the absence of a functional rom gene. We observed plasmid replication in the amino acid-starved pcnB relA double mutant. We propose a model for regulation of ColE1 replication in the amino acid-starved E. coli cells based on interactions between uncharged tRNA molecules and RNA I or RNA II. During starvation for different amino acids, different kinds of uncharged tRNA molecules appear in cells (they are much more abundant, however, in relA- mutants than in relA+ hosts) leading to various efficiencies of replication initiation. The Rom protein may modulate the effect of tRNA(s) by enhancing RNAI-RNA II, but not tRNA-RNA I and tRNA-RNA II, interactions.