Competition between sigma factors for core RNA polymerase

Abstract

The switch of RNA polymerase specificity from early to late promoters of bacteriophage T4 is achieved by substitution of host sigma factor, σ, with the T4 induced factor, σgp55. However, overproduction of σgp55 from an expression vector is not detrimental to Escherichia coli growth. Direct competition binding assays demonstrate that σ70 readily displaces σgp55 from RNA polymerase and thereby reverses the promoter specificity of the enzyme. The displacement also occurs with the core enzyme modified by bacteriophage T4 infection. We postulate that an antagonist of σ70 should be formed in T4-infected cells to aid σgp55σgp55 in the early/late switch. © 1987 IRL Press Limited, Oxford, England.