Helicases are molecular motors that use the energy of nucleoside 5'-triphosphate (NTP) hydrolysis to translocate along a nucleic acid strand and catalyse reactions such as DNA unwinding. The ring-shaped helicase¹ of bacteriophage T7 translocates along single-stranded (ss)DNA at a speed of 130 bases per second²; however, T7 helicase slows down nearly tenfold when unwinding the strands of duplex DNA³. Here, we report that T7 DNA polymerase, which is unable to catalyse strand displacement DNA synthesis by itself, can increase the unwinding rate to 114 base pairs per second, bringing the helicase up to similar speeds compared to its translocation along ssDNA. The helicase rate of stimulation depends upon the DNA synthesis rate and does not rely on specific interactions between T7 DNA polymerase and the carboxy-terminal residues of T7 helicase. Efficient duplex DNA synthesis is achieved only by the combined action of the helicase and polymerase. The strand displacement DNA synthesis by the DNA polymerase depends on the unwinding activity of the helicase, which provides ssDNA template. The rapid trapping of the ssDNA bases by the DNA synthesis activity of the polymerase in turn drives the helicase to move forward through duplex DNA at speeds similar to those observed along ssDNA.

1. Department of Biochemistry, UMDNJ-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, New Jersey 08854, USA
2. Department of Bio and Nanochemistry, Kookmin University, 861-1, Chongnung-dong, Songbuk-gu, Seoul 136-702, Korea
3. Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, Connecticut 06030-1507, USA

Correspondence to: Smita S. Patel¹ Correspondence and requests for materials should be addressed to S.S.P (Email: patelss@umdnj.edu).

Received 28 August 2004; Accepted 29 March 2005

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.