New tool for studying interactions of components of ribonucleic acid polymerase: rifampin-dependent mutants.

Mutants of Escherichia coli showing a rifampin-dependent phenotype were isolated from cells of strain CP78 mutagenized with ethyl methane sulfonate or nitrosoguanidine when an antibiotic underlay technique was used. The mutants varied greatly in their rifampin requirement. The minimum necessary concentration ranged from 1 to 50 micrograms/ml. The mutants could be divided into four phenotypic classes. These dependent mutants and their revertants should be a useful tool for probing interactions between the component polypeptides of ribonucleic acid polymerase and for studying the linkage of transcription with other cellular processes.