During phage morphogenesis, plays an essential role in the head-tail joining step (PubMed:32056848). The associated nuclease activity is essential for morphogenesis, possibly by cleaving packaged DNA to enable the joining of heads to tails (PubMed:32056848). Displays both exo- and endonuclease activity (PubMed:32056848). Belongs to the Caudovirales head completion nuclease family.