Cathleen L. Chan and Carol A. Gross§
From the Departments of Stomatology and of Microbiology and Immunology, University of California, San Francisco, California 94143
§ To whom correspondence should be addressed: University of
California, Campus Mailbox 0512, S-420,
513 Parnassus Ave., San Francisco, CA 94143. Tel.: 415-476-4161;
Fax: 415-476-4204;
E-mail: cgross@cgl.ucsf.edu
The anti-sequence, a portable element extending from +1 to +15 of the transcript, is sufficient to prevent promoter escape from a variety of strong s70 promoters. We show here that this sequence does not function with even the strongest s32 promoter. Moreover, a particular class of substitutions in s70 that disrupt interaction between Region 2.2 of 70 and a coiled-coiled motif in the b'-subunit of RNA polymerase antagonizes the function of the anti-element. This same group of mutants prevents lQ-mediated anti-termination at the lPR' promoter. At this promoter, interaction of s70 with the non-template strand of the initial transcribed sequence (ITS) is required to promote the pause prerequisite for anti-termination. These mutants prevent pausing because they are defective in this recognition event. By analogy, we suggest that interaction of s70 with the non-template strand of the anti-ITS is required for function of this portable element, thus explaining why neither s32 nor the Region 2.2 s70 mutants mediate anti-function. Support for the analogy with the lPR' promoter comes from preliminary experiments suggesting that the anti-ITS, like the lPR' ITS, is bipartite.
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