Cloning, overexpression and purification of a novel two-domain protein of Staphylococcus aureus phage Phi11

The genome of aureophage Phi11 reveals the presence of the gene gp07 which codes for the putative antirepressor protein (GenBank accession no. NC_004615.1). Antirepressor proteins are mainly involved in lytic cycle determination mechanisms of various bacteriophages. The Phi11 protein Gp07 consists of two domains-an amino terminal Bro domain and a carboxy terminal KilA domain. Despite the important role of antirepressor proteins in the developmental pathway of phages, there are no reports on the purification and characterization of aureophage antirepressor proteins. Here we describe a method to clone, overexpress and purify the full length Gp07 as carboxy terminal hexa histidine tag variant. The recombinant protein was expressed in Escherichia coli BL21(λDE3) cells and gradient of imidazole and NaCl were used for successful purification of the soluble recombinant protein to homogeneity. The protein exists as a dimer in solution as is evident from our gel filtration chromatography and glutaraldehyde cross-linking data. Further, we found that temperature has huge impact on the structural conformation of the protein. We expect that the purification of Gp07 will further our work in characterizing the role played by this protein during phage induction.