A novel form of suppression due to an altered RNA polymerase.

A group of mutants isolated from E coli K12(tif-1) display a very pleiotropic phenotype. The main characteristic of these mutants, temporarily designated 'S' strains, is their ability to suppress a large number of mutations. High efficiency of suppression is correlated with increased thermolability of cellular proteins, indicating an impairment in the fidelity of protein synthesis. Efficient suppression is also accompanied by the appearance of new characteristics like simultaneous resistance to several antibiotic drugs (Sm, Spc, and Mer), and plasmid-like DNA circles. Genetic studies show that the suppressor character is located in the rpoBC region. In a large number of spontaneous Rifr mutants, isolated from these strains, suppression or resistance to drugs is lost. The findings suggest that the phenotype of 'S' strains is due to an altered RNA polymerase causing erroneous transcription.