Plays a role in processing non linear or branched viral DNA intermediates in order to promote the production of mature packaged unit-length linear progeny viral DNA molecules. Exhibits endonuclease and exonuclease activities and accepts both double-stranded and single-stranded DNA as substrate. Exonuclease digestion of DNA is in the 5'-> 3' direction and the products are 5'-monophosphate nucleosides. Additionally, forms a recombinase with the major DNA-binding protein, which displays strand exchange activity. Also acts as a cytoplasmic RNA endonuclease that induces degradation of the majority of the cellular messenger RNAs during early lytic infection. The resulting inhibition of cellular protein synthesis serves to ensure maximal viral gene expression and evasion from host immune response. Internally cleaves host mRNAs which are then degraded by the cellular exonuclease XRN1. Bypasses therefore the regulatory steps of deadenylation and decapping normally required for XRN1 activation. Forms a complex with the DNA polymerase, the DNA polymerase processivity factor, and the major DNA binding protein. Belongs to the herpesviridae alkaline nuclease family.