DNA synthesis by a polymerase provides the driving force to accelerate DNA unwinding by a helicase

摘要

Helicases are molecular motors that use the energy of NTP hydrolysis to translocate along a nucleic acid strand and catalyze reactions such as DNA unwinding. The ring-shaped helicase of bacteriophage T7 translocates along single stranded (ss) DNA at a speed of 130 base per second. However, T7 helicase slows down nearly 10-fold when unwinding the strands of duplex DNA. Here we report that T7 DNA polymerase, unable to catalyze strand displacement DNA synthesis by itself, can increase the unwinding rate to 114 base pairs per second, bringing the helicase to similar speeds as along ssDNA. The helicase-rate stimulation depends upon the DNA synthesis rate and does not rely on specific interactions between the helicase and the polymerase. Efficient duplex DNA synthesis is achieved only by the combined action of the helicase and polymerase. The DNA polymerase depends on the unwinding activity of the helicase that 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.