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

Abstract

We provide evidence that, in terms of transcriptional organisation, the rpoBC operon carried by λrif ^d 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 β and β′ subunits of RNA polymerase) and rplL (coding for ribosomal proteins L7/L12) was cloned in a λ vector, and the resulting phage tested for gene expression. In common with the corresponding fragment of λrif ^d 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 λrif ^d 18, a sequence from the E. coli K12 chromosome which includes a promoter for these genes. As in λrif ^d 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 λrif ^d 18 results from more than one mutation.