Component of the viral DNA-dependent RNA polymerase that catalyzes two reactions involved in viral RNA cap formation: an RNA 5'-triphosphatase that hydrolyzes the gamma phosphate of triphosphate-terminated RNA and a guanylyltransferase that reacts with GTP to form a covalent protein-guanylate adduct. Therefore plays an essential role in late and very late gene expression. a 5'-end diphospho-ribonucleoside in mRNA + GTP + H(+) = a 5'-end (5'-triphosphoguanosine)-(ribonucleoside) in mRNA + diphosphate Interacts with LEF-8, LEF-9, and p47. Preferentially in the host nucleus and associated with the virogenic stroma. Belongs to the baculoviridae LEF-4 family.