Cloning of DNA of the rpoBC operon from the chromosome of Escherichia coli K12.

We provide evidence that, in terms of transcriptional organisation, the rpoBC operon carried by lambdarifd 18 accurately represents the corresponding region of the E. coli K12 chromosome. A restriction fragment of E. coli K12 chromosomal DNA carrying the genes rpoBC (encoding the beta and beta' subunits of RNA polymerase) and rplL (coding for ribosomal proteins L7/L12) was cloned in a lambda vector, and the resulting phage tested for gene expression. In common with the corresponding fragment of lambdarifd 18 DNA, the chromosomal fragment has no strong promoter for rplL or rpoBC transcription. Another new phage was constructed by adding, to the restriction fragment carrying the rplL rpoBC structural genes from lambdarifd 18, a sequence from the E. coli K12 chromosome which includes a promoter for these genes. As in lambdarifd 18 itself, this promoter is shared with rplJ but not with rplKA. The properties of the latter phage also show that the dominant rifampicin-resistance characteristic of lambdarifd 18 results from more than one mutation.