The
acid-soluble
ribonucleic acid degradation products formed by Escherichia coli cells starved for a
carbon source have been identified. They comprise
oligonucleotides,
nucleoside diphosphates, 5'- and 3'-nucleoside monophosphates,
nucleosides, and free bases. The majority of these products are excreted phates,
nucleosides, and free bases. The majority of these products are excreted into the medium, and only small and constant amounts are kept in the pool. During
carbon starvation at elevated temperatures, mutants deficient in
ribonuclease I do not form
oligonucleotides and 3'-nucleoside monophosphates, and mutants that contain a modified form of
polynucleotide phosphorylase do not accumulate
nucleoside diphosphates. 5'-Nucleoside monophosphates do accumulate, however, in a mutant containing thermoabile
ribonuclease II, under conditions where more than 95% of all
enzyme activity had been destroyed. The data presented confirm the participation of
ribonuclease I and
polynucleotide phosphorylase in the final steps of
ribonucleic acid degradation and indicate that an
exonuclease forming 5'-nucleoside monophosphates is also involved.