The stability of mRNA from the gsiB gene of Bacillus subtilis is dependent on the presence of a strong ribosome binding site

In Bacillus subtilis IS58 starved of glucose or exposed to heat shock, ethanol or salt stress, the sigma(B)-dependent general stress protein GsiB is accumulated to a higher level than other general stress proteins. This high-level accumulation of GsiB can at least partially be attributed to the remarkably long half-life (similar to 20 min) of the gsiB mRNA. Analysis of different gsiB-lacZ fusions revealed that this stability is not determined by sequences at the 3' end of the transcript but rather by sequences upstream of the translational start codon. Site-directed mutagenesis established that a strong ribosome binding site was crucial for the increased stability of the gsiB mRNA. A comparison of the sequences upstream of the translational start codons of three general stress genes, gsiB, gspA and ctc, revealed a direct correlation between mRNA stability and the strength of their translational signals.