Interactions of the bacteriophage T4 gene 55 product with Escherichia coli RNA polymerase. Competition with Escherichia coli sigma 70 and release from late T4 transcription complexes following initiation.

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The bacteriophage T4 gene 55 protein endows Escherichia coli RNA polymerase core with the ability to recognize T4 late promoters. In these experiments, we show that T4 gene product (gp) 55, like the major E. coli RNA polymerase initiation subunit sigma 70, is released from elongating transcription complexes and is thus capable of cycling among molecules of RNA polymerase core. We also show that, paradoxically, sigma 70 is able to displace T4 gp55 from its site of binding to E. coli RNA polymerase core. After T4 infection, the core enzyme is ADP-ribosylated in each alpha subunit, and a T4-coded 11.4-kDa protein (rpbA) binds tightly to it; these modifications do not save gp55 from displacement by sigma 70. However, open T4 late promoter complexes, containing gp55, are resistant to attack by sigma 70.