Published online 26 January 2005
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The herpes simplex virus type 1 DNA polymerase processivity factor, UL42, does not alter the catalytic activity of the UL9 origin-binding protein but facilitates its loading onto DNA
1 Department of Molecular Genetics, Immunology and Medical Genetics, Ohio State University Columbus, OH 43210, USA 2 Department of Molecular Virology, Immunology and Medical Genetics, Ohio State University Columbus, OH 43210, USA
*To whom correspondence should be addressed at Department of Molecular Virology, Immunology, and Medical Genetics, Ohio State University, 2198 Graves Hall, 333 West Tenth Avenue, Columbus, OH 43210, USA. Tel: +1 614 292 0735; Fax: +1 614 292 9805; Email: parris.1{at}osu.edu
Received September 13, 2004. Revised December 17, 2004. Accepted December 28, 2004.
The herpes simplex virus type 1 UL42 DNA polymerase processivity factor interacts physically with UL9 and enhances its ability to unwind short, partially duplex DNA. In this report, ATP hydrolysis during translocation of UL9 on single-stranded (ss) or partially duplex DNA was examined in the presence and absence of UL42 to determine the effect of UL42 on the catalytic function of UL9. Our studies reveal that a homodimer of UL9 is sufficient for DNA translocation coupled to ATP hydrolysis, and the steady-state ATPase catalytic rate was greater on partially duplex DNA than on ss DNA in the presence or absence of UL42. Although UL42 protein increased the steady-state rate for ATP hydrolysis by UL9 during translocation on either partially duplex or ss DNA, UL42 had no significant effect on the intrinsic ATPase activity of UL9. UL42 also had no effect on the catalytic rate of ATP hydrolysis when UL9 was not limiting but enhanced the steady-state ATPase rate at only subsaturating UL9 concentrations. At subsaturating UL9 to DNA ratios, stoichiometric concentrations of UL42 were shown to increase the amount of UL9 bound to ss DNA at equilibrium. These data support a model whereby UL42 increases the ability of UL9 to load onto DNA, thus increasing its ability to assemble into a functional complex capable of unwinding duplex DNA.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors
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