Ribosomes initiating translation of the hbs mRNA protect it from 5'-to-3' exoribonucleolytic degradation by RNase J1.

The discovery of the essential ribonuclease RNase J1, involved in global mRNA decay in Bacillus subtilis, has paved the way for studies on the turnover pathways of specific RNAs in this organism. Here we report an effect of RNase J1 depletion on both the maturation and degradation of the hbs mRNA, encoding the B. subtilis orthologue of the histone-like protein HU. The major hbs transcript observed in wild-type cells is generated by the blocking of 5'-to-3' exonuclease activity of RNase J1 by ribosomes initiating translation of this mRNA. Increasing the strength of the Shine-Dalgarno (SD) sequence leads to greater accumulation of this species, while weakening of the SD leads to its disappearance. The 5'-to-3' exonuclease activity of RNase J1 is also required for the turnover of the hbs mRNA, specifically the 3' half of the transcript. For both the maturation and degradation reactions, RNase J1 access to the mRNA requires prior endonucleolytic cleavage.