Figure 1. Structure and similarity of large T antigens.

A) Structure of the large T antigen protein. Functional domains (rectangles) within large T are depicted. The functions and percent amino acid identity (gray bar) of each domain within SV40 and JCV large T are indicated above the diagram. At the N-terminus are the DNA J domain and linker region, which are both required to fully inhibit pRB activity. The origin binding domain is required for the viral genome replication. The zinc binding domain and the ATPase domain together contribute to the helicase activity of large T. Cellular p53 binds large T through surface residues of the ATPase domain. The variable linker region and host range region are poorly characterized in comparison to the other regions of large T antigen. B) Structure of the large T antigen expressed from ERΔVHR constructs. The variable linker and host range region was removed from each TAg gene by PCR. These constructs express amino acids 1–625 of SV40 large T or amino acids 1–626 of JCV large T as well as other T antigen proteins (discussed in the Results). C) Protein sequence comparison of SV40 and JCV VHR regions. An alignment of amino acids was performed with LALIGN. The host range region of SV40 is highlighted in red letters, and was used to define the boundaries of the JCV host range region. Previously described motifs and post-translational modification sites are shown (described in the Discussion).