STRUCTURAL REQUIREMENTS OF BACILLUS-SUBTILIS SMALL CYTOPLASMIC RNA FOR CELL-GROWTH, SPORULATION, AND EXTRACELLULAR ENZYME-PRODUCTION

Bacillus subtilis small cytoplasmic RNA (scRNA; 271 nucleotides) is a member of the signal recognition particle (SRP) RNA family, which has evolutionarily conserved primary and secondary structures. The scRNA c onsists of three domains corresponding to domains I, II, and IV of hum an SRP 7S RNA. To identify the structural determinants required for it s function, we constructed mutant scRNAs in which individual domains o r conserved nucleotides were deleted, and their importance was assayed in vivo. The results demonstrated that domain TV of scRNA is necessar y to maintain cell viability. On the other hand, domains I and II were not essential for vegetative growth but were preferentially required for the RNA to achieve its active structure, and assembled ribonucleop rotein between Ffh and scRNA is required for sporulation to proceed. T his view is highly consistent with the fact that the presence of domai ns I and II is restricted to sporeforming B. subtilis scRNA among euba cterial SRP RNA-like RNAs.