Affiliation:
1. Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
Abstract
Activation of bacteriophage T4 middle promoters, which occurs about 1 min after infection, uses two phage-encoded factors that change the promoter specificity of the host RNA polymerase. These phage factors, the MotA activator and the AsiA co-activator, interact with theσ70specificity subunit ofEscherichia coliRNA polymerase, which normally contacts the −10 and −35 regions of host promoter DNA. Like host promoters, T4 middle promoters have a good match to the canonicalσ70DNA element located in the −10 region. However, instead of theσ70DNA recognition element in the promoter's −35 region, they have a 9 bp sequence (a MotA box) centred at −30, which is bound by MotA. Recent work has begun to provide information about the MotA/AsiA system at a detailed molecular level. Accumulated evidence suggests that the presence of MotA and AsiA reconfigures protein–DNA contacts in the upstream promoter sequences, without significantly affecting the contacts ofσ70with the −10 region. This type of activation, which is called ‘σappropriation’, is fundamentally different from other well-characterized models of prokaryotic activation in which an activator frequently serves to forceσ70to contact a less than ideal −35 DNA element. This review summarizes the interactions of AsiA and MotA withσ70, and discusses how these interactions accomplish the switch to T4 middle promoters by inhibiting the typical contacts of the C-terminal region ofσ70, region 4, with the host −35 DNA element and with other subunits of polymerase.
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50 articles.
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