A 5' stem-loop and ribosome binding but not translation are important for the stability of Bacillus subtilis aprE leader mRNA.

The Bacillus subtilis aprE leader is a determinant of extreme mRNA stability. The authors examined what properties of the aprE leader confer stability on an mRNA. The secondary structure of the aprE leader mRNA was analysed in vitro and in vivo, and mutations were introduced into different domains of an aprE leader-lacZ fusion. The half-lives of the corresponding transcripts were determined and beta-galactosidase activities were measured. Removal of a stem-loop structure at the 5' end or diminishing the strength of the RBS reduced the half-lives from more than 25 min to about 5 min. Interfering with translation by abolishing the start codon or creating an early stop codon had no or little effect on mRNA stability. The authors conclude that a 5' stem-loop and binding of ribosomes are necessary for the stability of aprE leader mRNA. The present results, together with a number of other data, suggest that translation of a B. subtilis mRNA is generally not important for its stability; the situation seems different in Escherichia coli. It is further concluded that the calculated strength of a B. subtilis RBS cannot be used to predict the stability of the corresponding transcript.