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Crystallization and X‐ray analysis of the transcription‐activator protein C1 of bacteriophage P22 in complex with the P RE promoter element
Author(s) -
Mondal Avisek,
Chattopadhyaya Rajagopal,
Datta Ajit Bikram,
Parrack Pradeep
Publication year - 2015
Publication title -
acta crystallographica section f
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 37
ISSN - 2053-230X
DOI - 10.1107/s2053230x15015708
Subject(s) - bacteriophage , transcription (linguistics) , tetramer , dna , crystallization , homotetramer , biology , promoter , lytic cycle , lysogenic cycle , activator (genetics) , microbiology and biotechnology , crystallography , chemistry , biophysics , genetics , gene , escherichia coli , biochemistry , protein subunit , gene expression , virus , linguistics , philosophy , organic chemistry , enzyme
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 (P RE ). 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 P 2 1 , 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.