Direct activator/co-activator interaction is essential for bacteriophage T4 middle gene expression.
The bacteriophage T4 AsiA protein is a bifunctional regulator that inhibits transcription from the major class of bacterial promoters and also serves as an essential co-activator of transcription from T4 middle promoters. AsiA binds the primary s factor in Escherichia coli, sigma(70), and modifies the promoter recognition properties of the sigma(70)-containing RNA polymerase(RNAP) holoenzyme. In its role as co-activator, AsiA directs RNAP to T4 middle promoters in the presence of the T4-encoded activator MotA. According to the current model for T4 middle promoter activation, AsiA plays an indirect role in stabilizing the activation complex by facilitating interaction between DNA-bound MotA and sigma(70). Here we show that AsiA also plays a direct role in T4 middle promoter activation by contacting the MotA activation domain. Furthermore,we show that interaction between AsiA and the beta-flap domain of RNAP is important for co-activation. Based on our findings, we propose a revised model for T4 middle promoter activation, with AsiA organizing the activation complex via three distinct protein-protein interactions.
Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., D1, Boston, MA 02115, USA.
Andy H
AH
Yuan
Ann
A
Hochschild
D017122:Bacteriophage T4 / Q000502:physiology*; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D008954:Models, Biological; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014764:Viral Proteins / Q000378:metabolism*
D004279:DNA, Viral; D004268:DNA-Binding Proteins; C067996:MotA protein, Enterobacteria phage T4; D014157:Transcription Factors; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase