[Frontiers in Bioscience 11, 2213-2223, September 1, 2006] 2213 The two helicases of herpes simplex virus type 1 (HSV-1) Soma Chattopadhyay, Yan Chen and Sandra K. Weller Molecular, Microbial and Structural Biology, University of Connecticut Health Center MC3205, 263 Farmington Ave, Farmington CT 06030 TABLE OF CONTENTS 1. Abstract 2.Introduction 3. Conserved helicase motifs present in all helicases 4. The origin binding protein UL9. 4.1. Interactions of UL9 with other viral and cellular proteins 4.2. UL9 is a weak helicase 4.3. Over expression of UL9 is inhibitory to HSV DNA replication 4.4. Regulation of UL9 protein levels and activity 5. The Helicase/Primase Complex UL5/8/52 5.1. The activities of the helicase/primase complex 5.2. UL5 is the putative helicase subunit 5.3. UL52 also is required for helicase activity 5.4. DNA binding of the UL5/8/52 complex 6. Viral helicases as targets for antiviral chemotherapy 7. Summary and future directions 8. Acknowledgments 9. References 1. ABSTRACT Herpes simplex virus type 1 (HSV-1) encodes two helicases both of which are essential for viral DNA synthesis. UL9 binds specifically to the origins of replication and is believed to initiate DNA replication at one of three origins of replication located in the HSV-1 genome. The heterotrimeric helicase-primase complex, encoded by the UL5, UL8 and UL52 genes, is believed to unwind duplex viral DNA at replication forks and to prime lagging strand synthesis. Functional analyses of UL9 and the helicase-primase complex will be discussed with attention to the roles these proteins play during HSV-1 replication. 2. INTRODUCTION Much of what we know today about helicases comes from the study of phage and viral systems primarily because these systems are amenable to genetic and biochemical analysis. The study of these viral helicases has greatly enhanced our understanding of the mechanisms of viral replication and has also provided powerful model systems for understanding the roles of helicases in cellular systems. Furthermore, several viral helicases are under consideration as potential targets for antiviral therapy (1-5). In this review, we focus on the helicases encoded by the herpesvirus family, primarily the two replicative helicases encoded by the herpes simplex virus type 1, UL5 and UL9. 3. CONSERVED MOTIFS ARE PRESENT IN ALL HELICASES Known and putative helicases contain common conserved motifs believed to play pivotal roles in their activities (6). Based on conserved motifs, helicases have been divided into three superfamilies (SF1, SF2, and SF3), the F4 family and a fifth small family of proteins represented by the bacterial transcription termination factor rho (6, 7). All five families of helicases contain signature Walker A and B box