Characterization of the RNA polymerase α subunit operon from Corynebacterium ammoniagenes

The rpoA gene, which encodes the α subunit of RNA polymerase, and the surrounding regions were cloned from Corynebacterium ammoniagenes (ATCC 6872), a parental strain of an industrial nucleotide producer in Korea. This region encodes genes for the following proteins (in order): initiation factor IF-1, the ribosomal proteins S13, S11 and S4, the α subunit of RNA polymerase and the ribosomal protein L17. Transcript mapping via reverse transcription polymerase chain reaction demonstrates that IF1, S13, S11, S4, α and L17 are transcribed as a polycistronic transcript from two tandem promoters preceding the IF-1 gene. The gene order of the C. ammoniagenes rpoA operon is characteristic of Corynebacteria. The rpoA gene encodes a protein of 334 amino acids with a deduced molecular weight of 35,971 Da, exhibiting 42 and 82% similarity to the Escherichia coli and Corynebacterium glutamicum α subunits, respectively. The regions that mediate interactions with β and β′ subunits and the residues that participate in the recognition of the UP element are conserved in the C. ammoniagenes α subunit. In contrast, there are differences between the C. ammoniagenes and E. coli α subunits in the residues assigned to the dimerization domain and the amino acids adjacent to conserved residues that mediate UP element recognition. The C. ammoniagenes rpoA gene expressed in E. coli complemented a temperature sensitive rpoA mutation, indicating that the C. ammoniagenes α subunit can function in E. coli .