Substrate specificity of an RNase III-like activity from Bacillus subtilis.

Bacillus subtilis bacteriophage SP82 codes for several early RNAs that were shown previously to be cleaved by an RNase III-like enzyme called "Bs-RNase III." Cloning of DNA fragments that encode these RNA sequences downstream of a T7 RNA polymerase promoter allowed the synthesis of substrates that were used to test the cleavage specificity of Bs-RNase III, which was purified from a protease-deficient strain of B. subtilis. Single nucleotide changes at or near the cleavage site and deletions upstream and downstream of the cleavage site were constructed. The effects of these changes on the rate of Bs-RNase III cleavage were measured. The activity of Bs-RNase III and Escherichia coli RNase III on heterologous substrates was also tested. Although the local environment of the site of Bs-RNase III cleavage appears very similar to that of E. coli RNase III, there are important differences in their substrate specificity.