Moderately thermostable phage Φ11 Cro repressor has novel DNA-binding capacity and physicochemical properties

Abstract

The temperate Staphylococcus aureus phage Φ11 harbors cI and cro repressor genes similar to those of lambdoid phages. Using extremely pure Φ11 Cro (the product of the Φ11 cro gene) we demonstrated that this protein possesses a single domain struc ture, forms dimers in solution at micromolar concentrations and maintains a largely α-helical structure even at 45o C. Φ11 Cro was sensitive to thermolysin at temperatures ranging from 55-75o C and began to aggregate at ~63o C, suggesting that the protein is moderately thermostable. Of the three homologous 15-bp oper ators (O1, O2, and O3) in the Φ11 cI-cro intergenic region, Φ11 Cro only binds efficiently to O3, which is located upstream of the cI gene. Our comparative analyses indicate that the DNA bind ing capacity, secondary structure and dimerization efficiency of thermostable Φ11 Cro are distinct from those of P22 Cro and λ Cro, the best characterized representatives of the two structurally different Cro families. [BMB reports 2009; 42(3): 160-165]