Studies on a mutant of Escherichia coli with unbalanced ribonucleic acid synthesis. II. The concomitance of ribonucleic acid synthesis with resumed protein synthesis.

A role of an intermediary agent in protein synthesis has been postulated for ribonucleic acid (RNA) (Brachet, 1955). However, the evidence for this hypothesis is still largely circumstantial and the details of the mechanism are unknown at the present time. In our studies on the lysogenie strain, Escherichia coli strain K12, we encountered an anomalous mutant which lends itself to a study of a possible relationship between RNA metabolism and protein synthesis. The auxotroph E. coli (K12 W-6) accumulates RNA during starvation of an essential nutrient, methionine (Borek et al., 1955). The RNA enriched organisms were found to be uniquely delayed in resuming protein synthesis after the restoration of the lacking amino acid (Borek et al., 1956). Moreover, such organisms are incapable of supporting the replication of infectious phage (Borek and Rockenbach, 1956 unpublished experiments). It seemed of interest to study the metabolism of RNA in these organisms before and at the time of the resumption of protein synthesis to ascertain whether any correlation between RNA metabolism and protein synthesis could be detected. It was found that the RNA accumulated on methionine starvation is stable after the restoration of the amino acid (recovery) in the sense that no extensive degradation of the polymer or excretion of RNA fragments could be detected. During the phase of recovery coinciding with the resumption of protein synthesis, significant net synthesis of RNA was observed. Such new synthesis in a bacterial cell which already con-