SV40 Large T Antigen Helicase/Initiator Structure and Function

Abstract

SV40 replication system serves as a model system for studying DNA replication in eukaryotic cells. SV40 large T antigen (LTag) is a replicative helicase and a “pleiotropic” replication initiator that recognizes replication origin, and initiates origin DNA melting and unwinding. To understand how LTag assembles on origin DNA to initiate DNA melting/unwinding, we determined the structure of the LTag‐dsDNA‐ADP complex, which represents the first structure for a hexameric helicase/initiator bound to dsDNA in the central channel. This structure captures a distinctive intermediate complex corresponding to an early stage of SV40 origin unwinding. The LTag‐DNA‐ADP complex structure reveals several unexpected features regarding: i) how a smaller hexameric channel accommodate a larger duplex DNA, ii) how the six subunits of LTag in the channel interact with dsDNA, and iii) how LTag distorts and melts the origin DNA using the β‐hairpin fingers and a nearby loop. I will present these new structural data and the implications for a plausible molecular mechanism for origin DNA melting and unwinding by this multi‐functional initiator and replicative helicase in eukaryotic cells.