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Bacteriophage phi X174-specific mRNA synthesis in cells deficient in termination factor rho activity

A previous report (Hayashi et al., Proc. Natl. Acad. Sci. U.S.A. 73:3519-3523, 1976) indicated that in vivo bacteriophage phi X174 mRNA's terminate after genes J, F, G, and H. However, termination at these sites is not stringent. To determine whether termination of phi X174 transcription depends on rho factor activity, we introduced a temperature-sensitive rho mutation (nitA) into a phi X174-sensitive host cell line and determined termination sites in wild-type and nitA cells. We found that (i) normal phi X174 terminators were recognized in phi X174-infected nitA cells, (ii) the rho mutation relieved polar effects caused by nonsense mutations in the phage genome or by chloramphenicol treatment of the host cells, and (iii) polarity was not caused by premature termination of transcription at the site of the polar mutation. RNA synthesis continued beyond the site to the first rho-sensitive site.