Nucleotide sequence and organization ofBacillus sublilisRNA polymerase major sigma (σ43) operon

The gene coding for Bacillus subtilis RNA polymerase major sigma 43, rpoD, was cloned together with its neighboring genes in a 7 kb EcoRI fragment. The complete nucleotide sequence of a 5 kb fragment including the entire rpoD gene revealed the presence of two other genes preceding rpoD in the order P23-dnaE-rpoD. The dnaE codes for DNA primase while the function of P23 remains unknown. The three genes reside in an operon that is similar in organization to the E. coli RNA polymerase major sigma 70 operon, which is composed of genes encoding small ribosome protein S21 (rpsU), DNA primase (dnaG), and RNA polymerase sigma 70 (rpoD). There is a relatively high degree of base and amino acid homology between the DNA primase and sigma genes. The most significant differences between the two operons are observed in the molecular size of the first genes (P23 and rpsU), the complete lack of amino acid homology between P23 and S21, the molecular weights of the two rpoD genes, the size of the intercistronic region between the first two genes, and the regulatory elements of the operon.