Open AccessChanging the mechanism of transcriptional activation by phage λ repressor
Author(s) -
Mei Li,
William R. McClure,
Miriam M. Susskind
Publication year - 1997
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.94.8.3691
Subject(s) - repressor , polymerase , microbiology and biotechnology , rna polymerase , rna polymerase ii , transcription (linguistics) , transcription factor ii d , mutant , biology , activator (genetics) , protein subunit , rna polymerase i , rna dependent rna polymerase , rna , promoter , enzyme , biochemistry , transcription factor , gene , gene expression , linguistics , philosophy
The first steps of transcription initiation include binding of RNA polymerase to a promoter to form an inactive, unstable, closed complex (described by an equilibrium constant,K B ) and isomerization of the closed complex to an active, stable, open complex (described by a forward rate constant,k f ). λ cI protein activates theP RM promoter by specifically increasingk f . A positive control mutant, cI-pc2, is defective for activation because it fails to raisek f . An Arg to His change in the σ70 subunit of RNA polymerase was previously obtained as an allele-specific suppressor ofcI-pc2 . To elucidate how the mutant polymerase restores the activation function of the mutant activator, abortive initiation assays were performed, using purified cI proteins and RNA polymerase holoenzymes. The change in σ does not significantly alterK B ork f in the absence of cI protein. As expected, cI-pc2 activates the mutant polymerase in the same way that wild-type cI activates the wild-type polymerase, by increasingk f . An unexpected and novel finding is that the wild-type activator stimulates the mutant polymerase, but not wild-type polymerase, by increasingK B .