Enzyme-catalyzed DNA unwinding. A DNA-dependent ATPase from E. coli

We have isolated a new DNA-dependent ATPase from E. coli. The enzyme has been purified to greater than 90% purity. It appears to be composed of two identical polypeptide chains of molecular weight 20,000. The enzyme catalyzed the hydrolysis of ATP in the presence, but not in the absence, of single-stranded DNA. Double-stranded DNA is not a cofactor. The products of hydrolysis are ADP and Pi. The enzyme also catalyzed strand separation of duplex DNA in the presence of ATP and E. coli DNA binding protein. Two E. coli proteins capable of promoting strand separation have been reported previously and have been termed helicase I and II (Abdel-Monem, M., and Hoffmann-Berling, H. (1977) Eur. J. Biochem. 79, 33-38). Accordingly, this protein is named helicase III.