A hairpin near the 5' end stabilises the DNA gyrase mRNA in Mycobacterium smegmatis.

RNA is amongst the most labile macromolecules present in the cells. The steady-state levels of mRNA are regulated both at the stages of synthesis and degradation. Recent work in Escherichia coli suggests that controlling the rate of degradation is as important as the process of synthesis. The stability of mRNA is probably more important in slow- growing organisms like mycobacteria. Here, we present our analysis of the cis elements that determine the stability of the DNA gyrase message in Mycobacterium smegmatis. The message appears to be stabilised by a structure close to its 5' end. The effect is especially pronounced in a nutrient-depleted state. These results largely parallel the model proposed in E.coli for mRNA degradation/ stability with subtle differences. Furthermore, these results suggest that the slow-growing organisms might use stable mRNAs as a method to reduce the load of transcription on the cell.