Polarity suppressors defective in transcription termination at the attenuator of the tryptophan operon of Escherichia coli have altered rho factor

Transcription termination factor rho purified from the polarity suppressor strains psu1, psu2 and psu4 is demonstrably different from wild-type rho. Rho factor from the mutant strains is more heat labile than wild-type rho. In addition, the ratio of transcription termination activity (Roberts, 1969) to RNA-dependent ATPase activity (Lowery-Goldhammer & Richardson, 1974) is reduced for all three suppressor strains; at ATPase levels where wild-type rho causes maximal inhibition of transcription (65%), psu1, psu2 and psu4 rho factors inhibit transcription 25, 50 and 15%, respectively. psu4 rho activity has altered chromatographic properties on DEAE-cellulose and sediments more slowly in glycerol gradients than does wild-type rho. Since psu1 and psu2 are defective in regulation of transcription termination at the tryptophan ( trp) operon attenuator (Korn & Yanofsky, 1976), we conclude that rho factor is essential for normal regulation at the trp attenuator. These results also indicate, in agreement with the findings of de Crombrugghe et al. (1973), Richardson et al. (1975), Ratner (1976) and Franklin & Yanofsky (1976) that rho-mediated transcription termination is the principal cause of mutational polarity.