Gene cluster rpoBC1C2 in cyanobacteria does not constitute an operon

The core enzyme of the cyanobacterial DNA-dependent RNA polymerase contains a unique component, γ, which is absent from the corresponding enzymes of other eubacteria. In the heterocystous cyanobacterium Nostoc commune the gene encoding γ, rpoC1, is immediately adjacent to, and downstream of, rpoB. The rpoC1 gene, and a 3′ adjacent gene, rpoC2, correspond to the single rpoC gene found in Escherichia coli with respect to those domains conserved within their translational products. Northern analysis and primer extension assay show that in N. commune, rpoC1 and rpoC2 are transcribed separately from rpoB. The promoter of rpoC1C2 can direct the expression of a promotorless lacZ gene in E. coli. As a consequence, cyanobacterial rpo gene expression is distinct from the mode of cotranscription described for the equivalent sequences found in other eubacteria, archaebacteria, and plant chloroplasts. Also in this paper, a simple protocol for RNA isolation, which should be applicable for RNA isolation from plant cells, is presented.