The catalytic element of a ribosomal RNA-processing complex

Abstract

The Bacillus subtilis RNase M5 complex, responsible for the terminal maturation of 5 S rRNA, includes two proteins. One of these proteins is ribosomal protein BL16 (equivalent to Escherichia coli EL18); the other, the alpha component, is required for catalysis. The RNase M5 alpha component has been purified in bulk extensively, and the active polypeptide (Mr approximately 24,000) identified following polyacrylamide gel electrophoresis. Reaction conditions (20-30% dimethyl sulfoxide) are reported which render RNase M5 activity independent of ribosomal protein BL16. This proves that alpha indeed is the catalytic element, the actual RNase M5, which normally attacks a ribonucleoprotein substrate consisting of protein BL16 in complex with the 5 S rRNA precursor. Kinetic analyses of the BL16-dependent and independent reactions suggest that any alpha-BL16 association contributes little to the energetics of the alpha-ribonucleoprotein substrate interaction. It is postulated that the BL16 protein serves as a scaffold, to lock the precursor mRNA into a conformation recognizable by the nuclease.