Characterization of the mRNA coding for ribonucleoside diphosphate reductase in Escherichia coli

Total Escherichia coli RNA was separated by electrophoresis on methyl mercury agarose gels, transferred to diazobenzyloxymethyl-paper, and hybridized to various DNA probes containing different segments of the nrd genes to determine the organization of these genes. A 3.2-kilobase polycistronic mRNA transcript which hybridizes to both the nrdA and nrdB genes indicated that the nrdA and nrdB genes are organized in an operon. The polycistronic transcript contained the nrdA gene at the 5' end and the nrdB gene at the 3' end. The size of the polycistronic mRNA was sufficient to code for the 80,000-molecular-weight B1 protein and the 40,000-molecular-weight B2 protein. The results also indicated that the nrdA and nrdB genes are the only genes in E. coli that code for ribonucleoside diphosphate reductase. Two smaller RNA species that hybridized to nrd DNA were observed and probably overlap with the 3.2-kilobase nrd mRNA.