REPLICATION OF PLASMIDS DERIVED FROM P1, F, R1, R6K AND RK2 REPLICONSIN AMINO ACID-STARVED ESCHERICHIA-COLI STRINGENT AND RELAXED STRAINS

Replication of mini-plasmids derived from bacteriophage P1 and natural ly existing plasmids F, R1, R6K and RK2 in otherwise isogenic relA(+) and relA(-) Escherichia coli strains during amino acid starvation and limitation was investigated. Since it was previously demonstrated that inhibition of DNA synthesis or amplification of plasmid DNA may depen d on the nature of deprived amino acid, we starved bacteria for five d ifferent amino acids. We found differential replication of all these p lasmids but RK2 (which did not replicate at all in amino acid-starved bacteria) during the stringent and relaxed response. While in almost a ll cases plasmid DNA replication was inhibited during the stringent re sponse irrespective of the nature of deprived amino acid, wild-type or copy-up mini-P1, mini-F and mini-Ri plasmids replicated in relA(-) ba cteria depending on the kind of starvation. R6K-derived plasmids harbo uring ori beta and gamma (but not those containing ori alpha, beta and gamma or only ori gamma) were able to replicate in relA(-) bacteria s tarved for all tested amino acids. Possible explanations fbr the mecha nisms of regulation of replication of plasmids derived from P1, F, R1: R6K and RK2 during amino acid starvation are discussed. Our results a lso indicate that, like in the case of some other replicons, appropria te amino acid starvation or limitation may be used as a method for eff icient amplification of plasmids derived from P1, F, R1 and R6K.