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The repressor protein and cognate operator DNA of any temperateStaph-ylococcus aureusphage have not been investigated in depth, despite having the potential to enrich the molecular biology of the staphylococcal system. In the present study, using the extremely pure repressor of temperate Staphylococcus aureusphage/11 (CI) | ỊFEBS Journal Physicochemical properties and distinct DNA binding capacity of the repressor of temperate Staphylococcus aureus phage 11 Tridib Ganguly Malabika Das Amitava Bandhu Palas K. Chanda Biswanath Jana Rajkrishna Mondal and Subrata Sau Department of Biochemistry Bose Institute Calcutta India Keywords dimer major groove operator phage 11 repressor CI Correspondence S. Sau Department of Biochemistry Bose Institute P1 12 - CIT Scheme VII M Calcutta 700 054 India Fax 91 33 2355 3886 Tel 91 33 2569 3200 E-mail subratasau@gmail.com These authors contributed equally to this work Received 20 November 2008 revised 16 January 2009 accepted 21 January 2009 doi 10.1111 j.1742-4658.2009.06924.x The repressor protein and cognate operator DNA of any temperate Staphylococcus aureus phage have not been investigated in depth despite having the potential to enrich the molecular biology of the staphylococcal system. In the present study using the extremely pure repressor of temperate Staphylococcus aureus phage 11 CI we demonstrate that CI is composed of a-helix and b-sheet to a substantial extent at room temperature possesses two domains unfolds at temperatures above 39 C and binds to two sites in the 11 cI-cro intergenic region with variable affinity. The above CI binding sites harbor two homologous 15 bp inverted repeats O1 and O2 which are spaced 18 bp apart. Several guanine bases located in and around O1 and O2 demonstrate interaction with CI indicating that these 15 bp sites are used as operators for repressor binding. CI interacted with O1 and O2 in a cooperative manner and was found to bind to operator DNA as a homodimer. Interestingly CI did not show appreciable binding to another homologous 15 bp site O3 that was located in the same primary immunity region as O1 and O2. Taken together these results suggest that 11 CI and the 11 CI-operator complex resemble significantly those of the lambdoid phages at the structural level. The mode of action of 11 CI however may be .
