title: Crystallization and X-ray analysis of the transcription-activator protein C1 of bacteriophage P22 in complex with the PRE promoter element.
abstract: The transcription-activator protein C1 of the temperate phage P22 of Salmonella typhimurium plays a key role in the lytic versus lysogenic switch of the phage. A homotetramer of 92-residue polypeptides, C1 binds to an approximate direct repeat similar to the transcription activator CII of coliphage λ. Despite this and several other similarities, including 57% sequence identity to coliphage CII, many biochemical observations on P22 C1 cannot be explained based on the structure of CII. To understand the molecular basis of these differences, C1 was overexpressed and purified and subjected to crystallization trials. Although no successful hits were obtained for the apoprotein, crystals could be obtained when the protein was subjected to crystallization trials in complex with a 23-mer promoter DNA fragment (PRE). These crystals diffracted very well at the home source, allowing the collection of a 2.2 Å resolution data set. The C1-DNA crystals belonged to space group P21, with unit-cell parameters a = 87.27, b = 93.58, c = 111.16 Å, β = 94.51°. Solvent-content analysis suggests that the asymmetric unit contains three tetramer-DNA complexes. The three-dimensional structure is expected to shed light on the mechanism of activation by C1 and the molecular basis of its specificity.
authors.affiliation: Department of Biochemistry, Bose Institute, P-1/12, CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Avisek
authors.initials: A
authors.lastname: Mondal
authors.affiliation: Department of Biochemistry, Bose Institute, P-1/12, CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Chattopadhyaya
authors.affiliation: Department of Biochemistry, Bose Institute, P-1/12, CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Ajit Bikram
authors.initials: AB
authors.lastname: Datta
authors.affiliation: Department of Biochemistry, Bose Institute, P-1/12, CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Pradeep
authors.initials: P
authors.lastname: Parrack
mesh_terms: D000595:Amino Acid Sequence; D017100:Bacteriophage P22 / Q000737:chemistry*; D002850:Chromatography, Gel; D003460:Crystallization; D018360:Crystallography, X-Ray; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D017386:Sequence Homology, Amino Acid; D014764:Viral Proteins / Q000737:chemistry*
chemical_list: D014764:Viral Proteins; C075601:transcription activator protein C1, Enterobacteria phage P22
keywords: P22 C1; lambda CII; lysis–lysogeny choice; phage P22