Daniel Simmons

Department of Biological Sciences

University of Delaware

213 McKinly Lab
Newark DE 19716-2590

Email: dsimmons@udel.edu
Phone: (302) 831-8547
Fax: (302) 831-2281

  • Ph.D., Biochemistry California Institute of Technology: 1974
    B.S., Chemistry, Colorado College: 1969

Research Overview:

Dr. Simmons’ laboratory is interested in the structure and function of the simian virus 40 tumor antigen (T antigen) and of cellular proteins that interact with it in virus infected and transformed cells. T antigen is a multifunctional phosphoprotein synthesized early in SV40 infection. It is required for virus DNA replication and for the regulation of viral gene expression in infected cells. The protein is also required for the induction and maintenance of malignant transformation of nonpermissive cells.

By using a multifaceted biochemical and genetic approach, they are investigating the fine structure and activity of various functional domains of T antigen and correlating this information to the biology of SV40. Their present effort is focused primarily on T antigen’s role in the initiation and elongation phases of SV40 DNA replication. This viral protein is a helicase and is needed to melt the origin of replication. They have obtained evidence that topoisomerase I forms a complex with a double hexamer of T antigen to initiate DNA replication. This complex is believed to act as a swivelase to unwind and simultaneously relax DNA during replication. The presence of a eukaryotic topo I appears to be absolutely required for unwinding of circular DNA. Other proteins such as RPA and DNA polymerase a/primase probably associate with the initiation complex after topo I and T antigen have bound to the origin of replication. The major aims are to understand the mechanism by which T antigen participates in the replication of virus DNA in infected cells and to determine the structure and composition of the initiation and replication complexes.

Another major aim of Dr. Simmons’ research is to determine the three-dimensional structure of this important viral helicase. To date, only the structures of the DNA binding domain and of the “J” domain have been determined. They are overexpressing full-length T antigen as well as fragments of T antigen in baculovirus infected insect cells and purifying these proteins in order to crystallize them and determine their tertiary and quaternary structures.