Replication of Plasmids during Bacterial Response to Amino Acid Starvation

Amino acid starvation of bacterial cells leads to expression of the stringent (in wild-type strains) or relaxed (inrelAmutants) response (also called the stringent or relaxed control, respectively). The stringent control is a pleiotropic response which changes drastically almost the entire cell physiology. Although starvation is a rule rather than an exception in natural environments of bacteria, and DNA replication is a fundamental cell process, until recently our knowledge about regulation of DNA replication in amino acid-starved cells has been unexpectedly poor. Within recent years the stringent control of DNA replication has been investigated mainly on plasmid models. Several plasmid replicons have been studied, includingoriCplasmids, ColE1-like replicons, pSC101, F, R1, RK2, and R6K, and plasmids derived from bacteriophages λ and P1. However, molecular models of replication regulation in amino acid-starved cells have been proposed to date only for λ plasmids and ColE1-like replicons. Although further extensive studies are necessary in the understanding of molecular mechanisms of the stringent and relaxed control of replication of other plasmids, the results obtained to date (summarized and discussed in this review) show that studies on DNA replication in amino acid-starved cells may provide new insights into the regulatory mechanisms and lead to more general conclusions.