Differential inhibition of the initiation of DNA replication in stringent and relaxed strains ofEscherichia coli

Abstract

SummaryStarvation for isoleucine inhibits chromosome, minichromosome and pBR322 DNA replication in a stringent strain ofE. coli, but does not do so in a relaxed mutant. Starvation for other amino acids inhibits either chromosome and minichromosome replication in both strains. From these results we conclude thatoriCand pBR322 replication are stringently regulated and that isoleucine seems not to be essential for the protein synthesis required at the initiation oforiCreplication. Deprivation of isoleucine in a Rel−strain gives rise to amplification of minichromosome and pBR322 with a better yield of the latter plasmid than that following treatment with chloramphenicol.