Essential serine/threonine-protein kinase that plays different role in the viral life cycle. Phosphorylates the host small ribosomal protein RACK1 thereby customizing the ribosomes to a state optimal for viral mRNAs (which contain poly-A leaders) but not for host mRNAs. Facilitates viral DNA replication by inhibiting host BANF1, a cellular host defense responsive to foreign DNA. Phosphorylates host BANF1 on serine and threonine residues; this leads to BANF1 relocalization to the cytoplasm, loss of dimerization and impaired DNA binding activity. Indeed, BANF1 activity depends on its DNA-binding property which is blocked by VPK1-mediated phosphorylation. Required for viral intermediate genes expression, probably by inhibiting host BANF1. Modulates cellular responses via host JUN by two different mechanisms, either by direct phosphorylation or by modulation of upstream JIP1-MAPK complexes. Seems to participate in the accumulation/processing of late proteins and thus in virion maturation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with host JIP1; this interaction increases the amount of MAPK bound to JIP1 and subsequently increases the activity of transcription factors, such as JUN, that respond to these complexes. Localizes in cytoplasmic viral factories and is a minor component of the virion. Autophosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Poxviruses subfamily.