Role of the RNA polymerase α subunit in transcription activation

SummaryThe N‐terminal two‐thirds of the α subunit of Escherichia coli RNA polymerase plays an essential role in the initiation of subunit assembly, by gathering two large subunits, β and β', together into a coreenzyme complex. One group of RNA polymerase mutants deficient in response to transcription activation carries mutations in the C‐terminal region of the α subunit, indicating that the C‐terminal region of the a subunit is involved in protein‐protein contact in positive control of transcription. A set of activators (class I transcription factors) which make contact with this contact site I region on RNA polymerase a subunit bind in most cases to DNA upstream of the promoter ‐35 signal. Genetic fine mapping indicates that a cluster of subsites exists in the contact site I region, each interacting with a set of the class I factors and each consisting of a structure formed by only 5‐10 amino acid residues.