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Molecular and Cellular Biology, August 2002, p. 5669-5678, Vol. 22, No. 16
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.16.5669-5678.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Role of the p68 Subunit of Human DNA Polymerase -Primase in Simian Virus 40 DNA Replication

Robert D. Ott, Christoph Rehfuess,^, Vladimir N. Podust, Jill E. Clark,^, and Ellen Fanning^*

Department of Biological Sciences and Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37232

Received 12 March 2002/ Returned for modification 15 April 2002/ Accepted 20 May 2002

DNA polymerase -primase (pol-prim) is a heterotetramer with DNA polymerase and primase activities. The polymerase (p180) and primase (p48 and p58) subunits synthesize primers and extend them, but the function of the remaining subunit (p68) is poorly understood. Genetic studies in yeast suggested an essential role for the p68 ortholog in early S phase prior to the hydroxyurea-sensitive step, possibly a regulatory role in initiation of DNA replication, but found no evidence for an essential function of p68 later in S phase. To investigate whether the human p68 subunit has an essential role in DNA replication, we examined the ability of a purified trimeric human pol-prim lacking p68 to initiate simian virus 40 DNA replication in vitro and to synthesize and elongate primers on single-stranded DNA in the presence of T antigen and replication protein A (RPA). Both activities of trimeric pol-prim were defective, but activity was recovered upon addition of separately purified p68. Phosphorylation of p68 by cyclin A-dependent protein kinase also inhibited both activities of pol-prim. The data strongly suggest that the p68 subunit is required for priming activity of pol-prim in the presence of RPA and T antigen, both during initiation at the origin and during lagging strand replication.

Present address: Wilramstr. 25, D-81669 Munich, Germany.

Present address: 1727 Todd Dr., Johnson City, TN 37604.

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