Crystal structure of bacteriophage lambda cII and its DNA complex

摘要

The tetrameric cll protein from bacteriophage lambda activates transcription from the phage promoters P-RE, P-i, and P-AQ by binding to two direct repeats that flank the promoter -35 element. Here, we present the X-ray crystal structure of cll alone (2.8 angstrom resolution) and in complex with its DNA operator from PRE (1.7 angstrom resolution). The structures provide a basis for modeling of the activation complex with the RNA polymerase holoenzyme, and point to the key role for the RNA polymerase alpha subunit C-terminal domain (alpha CTD) in cll-dependent activation, which forms a bridge of protein/protein interactions between cll and the RNA polymerase sigma subunit. The model makes specific predictions for protein/protein interactions between cll and alpha CTD, and between aCTD and sigma, which are supported by previous genetic studies.