DYNAMIC PHOSPHORYLATION OF AUTOGRAPHA-CALIFORNICA NUCLEAR POLYHEDROSIS-VIRUS PP31

Autographa californica nuclear polyhedrosis virus (AcMNPV) pp31 is a n uclear phosphoprotein that accumulates in the virogenic stroma, which is the viral replication center in the infected-cell nucleus, binds to DNA, and serves as a late expression factor, Considering that reversi ble phosphorylation could influence its functional properties, we exam ined phosphorylation and dephosphorylation of pp31 in detail, Our resu lts showed that pp31 is posttranslationally phosphorylated by both cel lular and virus-encoded or -induced kinases. Threonine phosphorylation of pp31 by the virus-specific kinase activity was sensitive to aphidi colin, indicating that it requires late viral gene expression. We also found that pp31 is dephosphorylated by a virus-encoded or -induced ph osphatase(s), indicating that phosphorylation of pp31 is a dynamic pro cess, Analysis of pp31 fusion proteins showed that pp31 contains at le ast three phosphorylation sites, The amino-terminal 100 amino acids of pp31 include at least one serine residue that is phosphorylated by a cellular kinase(s). The C-terminal 67 amino acids of pp31 include at l east one threonine residue that is phosphorylated by the virus-specifi c kinase(s). Finally, this C-terminal domain of pp31 includes at least one serine that is phosphorylated by either a host or viral kinase(s) , Interestingly, site-directed mutagenesis of the consensus threonine phosphorylation sites in the C-terminal domain of pp31 failed to preve nt threonine phosphorylation, suggesting that the virus-specific kinas e is unique and has an undetermined recognition site.