Synthesis and degradation of lac mRNA in E. coli depleted of 30S ribosomal subunits

Escherichia coli was depleted of active ribosomes by a thermal shock at 47°C which quantitatively destroyed the 30S ribosomal subunits. During recovery, RNA is synthesized while protein synthesis resumes only after about 90 minutes. It is shown that lac mRNA is synthesized in the complete absence of ribosomal activity and hence RNA synthesis is not coupled to protein synthesis. Transcription time and average transcript length were slightly less than in untreated cells. lac mRNA was degraded much more slowly in bacteria depleted of ribosomes. In E. coli W both functional half life (T_1/2=28 min vs. 2.25 in untreated cells) and chemical stability (T_1/2=32 min vs. 7 in untreated cells) was increased. The analysis of rna and pnp mutants showed that polynucleotide phosphorylase is involved in lac mRNA degradation in heat treated cells but that RNase I is not. The functional T 1/2 was increased in pnp mutants and was 95 min during the recovery period. The rate of chemical decay is so slow that the half-life cannot be accurately determined.