Cell
Volume 29, Issue 3, July 1982, Pages 939-944
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Article
Promoter occlusion: Transcription through a promoter may inhibit its activity

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Abstract

Induction of prophage lambda inhibits the expression of the gal operon from its cognate promoters. The effect is observed only in cis, and is due to frequent transcription of the gal promoter region by RNA polymerase molecules initiating upstream at the prophage PL promoter. The frequency of transcription initiation at PL is some 30 times greater than that at the gal promoter, Pg1. PL is one of the strongest procaryotic promoters. This “promoter occlusion” is essentially complete when the distance between gal and PL is small (≤10 kb); and when PL is fully active (that is, in the absence of the cl or cro repressors). We discuss the possibility that promoter occlusion at two lambda promoters, Pint and PR′, might play a role in the sequential expression of viral functions.

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