Involved in the co-transcriptional or post-transcriptional endoribonucleolytic cleavage that generates sequence-homogeneous 3' ends during late transcription. Involved in postreplicative transcription elongation on intermediate and late genes (Probable). Also involved in DNA replication and in multiple steps of virion morphogenesis. Required both for inclusion of virosoplasm into crescents as well as for maturation of immature virions (IV) into mature virions (MV). Interacts with the DNA polymerase processivity factor A20. Interacts with B1R kinase. Interacts with the late transcription factors VLTF-1 AND VLTF-3. Interacts with the late transcription elongation factor G2. Interacts with itself. Might be part of a transcription complex composed at least of G2, A18, and H5. Early during viral infection, diffusely localizes within the cytoplasm. Following DNA replication, localizes specifically to virus factories. Constitutively expressed in abundance during viral replication. Phosphorylated at multiple sites. Phosphorylation is necessary for cleavage activity. Phosphorylated by the viral B1R and F10 kinases (Probable). Belongs to the chordopoxvirinae protein H5 family. Was originally thought to be p35/Ag35, a membrane protein involved in the biogenesis of the viral envelope encoded by H3L gene.