THE DEAD-Box PROTEIN Csha IN STAPHYLOCOCCUS AUREUS CONTAINS ATP-INDEPENDENT DNA STRAND ANNEALING AND EXCHANGE ACTIVITIES

DEAD-box proteins (DBPs) that are usually RNA helicases have important roles in eukaryotic and bacterial RNA metabolism. Recent studies have reported that certain prokaryotic DBPs exhibit ATP-independent nucleic acid displacement and annealing activities. We investigated one putative RNA helicase, CshA DEAD-box protein, from vancomycin-resistant Staphylococcus aureus strain Mu 50 for ATP-independent activities on nucleic acids. We herein report that CshA has two novel ATP-independent activities - annealing of complementary single-stranded DNA (ssDNA) and strand exchange on short double-stranded DNA (dsDNA). These DNA strand annealing and exchange activities are independent of Mg2+ ion or ATP binding and hydrolysis. ssDNA annealing activity as well as versatile DNA strand exchange activity of CshA suggests a possible role in dsDNA break repair processes.