What is the role of RNase J in mRNA turnover?

The discovery of the paralogous ribonucleases J1 and J2 has been a major advance in the study of RNA maturation and decay in Bacillus subtilis and related organisms. RNase J1 was the first bacterial enzyme shown to possess 5'-to-3' exoribonuclease activity, reversing a dogma that suggested this type of activity was unique to eukaryotic mRNA decay. RNase J1 and J2 form a complex that also has endonuclease activity and these enzymes have been shown to play a key role in the turnover and maturation of many RNAs in B. subtilis. Here, I describe recent progress in our understanding of the role of these enzymes in RNA metabolism in this organism and argue that the 5'-to-3' exoribonuclease activity may be the more important of the complex's two modes of action.