Relationship of oligomerization to enzymatic and DNA-binding properties of the SV40 large T antigen.

Crude and highly purified SV40 large T antigen has been found to exist in forms of various sizes Immunoreactive structures of 5.5S (80-85 kd), 7S (or approximately 150 kd) and 15.5S (325-340 kd) have been identified by zonal sedimentation and gel filtration. They appear to correspond to monomeric, dimeric and tetrameric species of T, respectively, and are free of detectable 55 kd NVT by specific immunoprecipitation analyses. While highly purified monomer appears relatively inactive in SV40 DNA-binding and ATPase assays, both the dimer and tetramer display these activities. By contrast, all three comigrate with casein kinase activity. These data suggest that the protein can exist as a monomer and in various homoaggregated forms. In addition, it appears that it must aggregate to be an active DNA-binding element and an ATPase.