TRANSCRIPTIONAL ACTIVATION BY A DNA-TRACKING PROTEIN - STRUCTURAL CONSEQUENCES OF ENHANCEMENT AT THE T4 LATE PROMOTER

Transcriptional initiation at bacteriophage T4 late promoters is activ ated from enhancer-like distal sites by the T4 gene 44, 62, and 45 DNA polymerase accessory proteins (gp44, gp62, and gp45, respectively). E nhancement is ATP hydrolysis-dependent and requires protein tracking a long DNA. The structural analysis of the entranced transcription initi ation complex shows gp45 located at the upstream end of this promoter complex in the vicinity of its transcriptional coactivator, the T4 gen e 33 protein. The ATP-cleaving gene 44 protein-gene 62 protein complex serves as the assembly factor for gp45, but does not stably associate with the enhanced promoter complex. Transcriptional enhancement quant itatively favors, but does not qualitatively change, DNA strand separa tion in the transcription bubble. A model of the transcriptional activ ation that rationalizes its DNA-tracking and activation-polarity prope rties is presented.