POLYADENYLYLATION HELPS REGULATE MESSENGER-RNA DECAY IN ESCHERICHIA-COLI

As part of our genetic analysis of mRNA decay in Escherichia coli K-12 , we examined the effect of the pcnB gene [encoding poly(A) polymerase I] on message stability. Eliminating poly(A) polymerase I (Delta pcnB ) dramatically stabilized the lpp, ompA, and trxA transcripts. The hal f lives of individual mRNAs were increased in both a Delta pcnB single mutant and a Delta pcnB pnp-7 rnb-500 rne-1 multiple mutant. We also found mRNA decay intermediates in Delta pcnB mutants that were not det ected in control strains, By end-labeling total E. coli RNA with [P-32 ]pCp and T4 RNA ligase and then digesting the RNA with RNase A and T-1 , we showed that many RNAs in a wild-type strain contained poly(A) tai ls ranging from 10 nt to >50 nt long. When polynucleotide phosphorylas e, RNase II, and RNase E were absent, the length (>100 nt) and number (10- to 20-fold) of the poly(A) tails increased. After transcription i nitiation was stopped with rifampicin, polyadenylylation apparently co ntinued. Deleting the structural gene for poly(A) polymerase I (pcnB) reduced the amount of 3'-terminal poly(A) sequences by >90%. We propos e a model for the role of polyadenylylation in mRNA decay,