RIF(R) MUTATIONS IN THE BEGINNING OF THE ESCHERICHIA-COLI RPOB GENE

In Escherichia coli, mutations conferring rifampicin (Rif) resistance map to the rpoB gene, which encodes the 1342-amino acid beta subunit o f RNA polymerase. Almost all sequenced Rif(R) mutations occur within t he Rif region, encompassing rpoB codons 500-575. A strong Rif(R) mutat ion lying outside the Rif region, which changed Val(146) to Phe was pr eviously reported, but was not recovered in subsequent studies. Here, we used site-directed mutagenesis followed by selection on Rif to sear ch for Rif(R) mutations in the evolutionarily conserved segment of rpo B around codon 146. Strong Rif(R) mutations were obtained when Va1146 was mutated, and several weak Rif(R) mutations were also isolated near position 146. The results define a new, N-terminal cluster of Rif(R) mutations, in addition to the classical central Rif region.