The DNA sequence of the gene (rnc) encoding ribonuclease III ofEscherichia coli

Abstract

The DNA sequence of a 1,076 base pair Bg1I-BamHI fragment containing the entire rnc gene for ribonuclease III (RNase III) was determined. An open reading frame of 681 base pairs was found in this region which encodes a protein of 227 amino acid residues (calculated molecular weight = 25,218). When this open reading frame was cloned into a high expression vector, pIN-III, a protein of apparent molecular weight of 26,000 was produced upon induction of the cloned gene. This product accounted for up to 5% of the total cellular protein, and comigrated with purified RNase III. RNase III enzyme activity was induced in parallel with the production of the 26,000 molecular weight protein. A putative promoter was found 170 base pairs upstream from the initiation codon. In the long leader region a very stable stem-bulge-stem structure was found which closely resembles typical RNase III cleavage sites. This structure may be cleaved by RNase III to auto-regulate the expression of the rnc gene.