Seung-Jae Leea,b,c, Salman Syedd, Eric J. Enemarka,c,1, Stephen Schuckc, Arne Stenlundc, Taekjip Had,e,2, and Leemor Joshua-Tora,b,c,2
aW. M. Keck Structural Biology Laboratory,
bHoward Hughes Medical Institute, and
cCold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724; and
dCenter for Biophysics and Computational Biology and
eDepartment of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana?Champaign, Urbana, IL 61801
A prerequisite for DNA replication is the unwinding of duplex DNA catalyzed by a replicative hexameric helicase. Despite a growing body of research, key elements of helicase mechanism remain under substantial debate. In particular, the number of DNA strands encircled by the helicase ring during unwinding and the ring orientation at the replication fork completely contrast in contemporary mechanistic models. Here we use single-molecule and ensemble assays to address these questions for the papillomavirus E1 helicase. We find that E1 unwinds DNA with a strand-exclusion mechanism, with the N-terminal side of the helicase ring facing the replication fork. We show that E1 generates strikingly heterogeneous unwinding patterns stemming from varying degrees of repetitive movements, which is modulated by the DNA-binding domain. Together, our studies reveal previously unrecognized dynamic facets of replicative helicase unwinding mechanisms.
ATPase, molecular motors
1Present address: Department of Structural Biology, St Jude Children’s Research Hospital, Memphis, TN 38105.
2To whom correspondence may be addressed.
Author contributions: S.-J.L., E.J.E., A.S., T.H., and L.J. designed research; S.-J.L., S. Syed, E.J.E., S. Schuck, and A.S. performed research; S.-J.L. contributed new reagents/analytic tools; S.-J.L., S. Syed, E.J.E., S. Schuck, A.S., T.H., and L.J. analyzed data; and S.-J.L., E.J.E., A.S., T.H., and L.J. wrote the paper.