[Methylation of E. coli RNA polymerase with dimethylsulfate]

DNA dependent RNA polymerase from E. coli was methylated with dimethylsulfate. After the methylation the enzymatic activity was lost. Addition of two methyl groups per enzyme monomer completely inactivated enzyme with respect to RNA synthesis but couldn't prevent enzyme binding to DNA. Methylated enzyme was able to form tight complexes with DNA and to compete with the native enzyme for the formation of rifampicin resistant complex with DNA. The ratio of the binding constants of the native and methylated enzymes to DNA was determined to be equal to 3. Methylated enzyme was not able to form the first phosphodiester bound as revealed from pyrophosphate exchange reaction studies.