Amino acid starvation in an Escherichia coli auxotroph : I. Effects on protein and nucleic acid synthesis and on cell division

Abstract

We have studied the effects of amino-acid starvation and subsequent refeeding in a leucine auxotroph of Escherichia coli, K- i2. During starvation, protein and RNA synthesis cease but DNA synthesis continues to a limited extent and half the cells divide. Ribonucleotides accumulate within the cells and related substances are excreted into the medium. After 90 min starvation, supplying leucine again causes immediate resumption of protein, RNA, and DNA synthesis. Cell division, however, only resumes after a lag of one-quarter to one-half generation time. During this lag most of the cells become unusually vulnerable to death by dehydration. We have discussed these findings with reference to events in the cell growth and division cycle. The normal synthesis of RNA appears to require concomitant protein synthesis. DNA synthesis does not absolutely require concomitant protein or RNA synthesis, but the amount of DNA synthesized under such conditions is far less than would result from a single replication. It appears that about half of the normal growth cycle in Escherichia coli entails preparations for cell division that do not require concomitant protein or RNA synthesis.