The problem of mRNA decay in E. coli has
recently seen exciting progress, with the discoveries that
key degradation enzymes are associated together in a high
molecular weight degradosome and that polyadenylation promotes
decay. Recent advances make it clear that mRNA decay in
bacteria is far more interesting enzymatically than might
have been predicted. In-depth study of specific mRNAs has
revealed multiple pathways for degradation. Which pathway
a given mRNA follows appears to depend in large part on
the location of the initiating endonucleolytic cleavage
within the mRNA. During the steps of mRNA decay, stable
RNA structures pose formidable barriers to the 3′
→ 5′ exonucleases. However, polyadenylation
is now emerging as a process that plays an important role
in maintaining the momentum of exonucleolytic degradation
by adding single-stranded extensions to the 3′ ends
of mRNAs and their decay intermediates, thereby facilitating
further exonuclease digestion.