SV40 large T antigen (LT) is a potent carcinogen, and plays an essential role for SV40 DNA replication as the replicative helicase and replication initiator protein. SV40 replication serves as a model for eukaryotic DNA replication, as SV40 uses all the essential cellular replication proteins (primase, polymerase, PCNA, Topoisomerases, etc.), except for the helicase and cellular initiator proteins that consist of multiple initiator factors (such as Orc, Ctd1, Cdc6, MCM in eukaryotes, or DnaA/DnaC/DnaB in prokaryotes) to initiate DNA replication, i.e. marking the replication origin, recruiting helicase, melting origin, and activating helicase. For SV40 replication, LT alone fulfills essentially all the initiator functions and is the helicase for replication fork unwinding during elongation phase. The long-term goal of this research is to understand how LT functions as a helicase to coordinate the functions of the other replication proteins for DNA replication, as well as how LT transforms cells.
Specific aims are designed to understand how LT hexameric and double hexameric helicase melt the origin DNA and unwinds dsDNA to initiate DNA replication. We plan to use mainly X-ray protein crystallography, assisted with EM and AFM, single molecule assay, computational method, molecular biology and functional biochemistry in vitro and in cells. The results from this research are expected to have potential impact on the field of DNA replication in eukaryotic cells and on cancer biology.

Public Health Relevance

SV40 large T (LT) has remarkably diverse biological activities. Besides its ability to regulate many aspects of viral infection and cellular processes, LT in its hexameric and double hexameric forms is an efficient molecular machine that can melt dsDNA and unwind replication forks for DNA replication. LT is the only viral protein required for SV40 minichromosome DNA replication, all the rest proteins are from cellular replication machinery in mammalian cells. In this minichromosome replication, LT performs the functions of the cellular helicase MCM and several other initiator proteins for origin localization and melting. As a result, SV40 replication system has been serving as a model system for studying eukaryotic replication. The study of LT helicase mechanisms will have general implications for understanding other replicative helicases, especially for those from eukaryotic cells.
We aim to understand the detailed molecular mechanisms of the helicase function of LT hexameric and double hexameric machine. The data generated from this research will provide valuable information about helicase function and DNA replication. This study bears high relevance to cancer biology.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI055926-10
Application #
8293210
Study Section
Virology - A Study Section (VIRA)
Program Officer
Park, Eun-Chung
Project Start
2003-07-01
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
10
Fiscal Year
2012
Total Cost
$503,483
Indirect Cost
$173,284
Name
University of Southern California
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
072933393
City
Los Angeles
State
CA
Country
United States
Zip Code
90089
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