Replication activity of JC virus large T antigen phosphorylation and zinc finger domain mutants.

The replication potential of the human polyomavirus JC virus (JCV) relative to that of the related monkey virus SV40 is limited, in part, by differences in the multifunctional T antigen (T Ag). Earlier genetic analyses of the SV40 T protein indicated that specific phosphorylation sites and a zinc finger motif are involved in the regulation of viral replication. The JCV and SV40 T Ags differ with respect to sequences encoding these functional domains, and in the present study mutational analysis of the JCV protein was conducted to assess the role that unconserved residues might play in the restricted lytic behavior of JCV. Amino acids Asn316 and His317 in the zinc finger domain and Thr664 and Glu666 in the carboxy-terminal phosphorylation domain were mutated to either an SV40-like residue or an alanine. Each of the mutant JCV genomes replicated with wild type efficiency suggesting that, unlike the case for SV40 T Ag, these amino acids are not critical to the regulation of viral replication. On the other hand, mutation of amino acid Thr125 within the amino-terminal phosphorylation domain abolished JCV DNA replication and viability. This site is conserved in the SV40 T Ag, and previous results have revealed that phosphorylation of this residue (Thr124) is required for T Ag replication function.