| Comments |
"In quantitative terms, where does RNase E invest its enzymatic turnovers? This can be estimated with the following assumptions. In a culture of Escherichia coli K12 that grows with a doubling time of about 30 minutes, there will be approximately 50,000 ribosomes [BNID 111527], 375,000 tRNAs [BNID 108611] (7.5 per ribosome) and perhaps a single to at most ten copies of each of the ~2,000 mRNAs per cell. Each mRNA is assumed to be transcribed 5–10 times per
generation (BNID 111529)(thus, ~30,000 mRNA transcripts per generation, assuming that there are three
copies of each mRNA and these are each transcribed five times per generation). To a first
approximation, RNase E must make 150,000 cleavages in rRNA precursors, 248,000 cleavages in tRNA precursors and up to 90,000 cleavages in mRNAs (assuming three per mRNA) during every generation [BNID 111530]. This workload, 16,000 cleavage events per minute, is fully consistent with an estimate of about 1,470 copies of RNase E per cell (32% of the RNA polymerase content [refs 90,114]) and a turnover of 11 cleavage events per RNase E per minute (REF. 42 determined with an artificial substrate at 30 °C)." |