Endolysin that degrades host peptidoglycans and participates with the holin protein(s) in the sequential events which lead to the programmed host cell lysis releasing the mature viral particles. Once the holin(s) has permeabilized the host cell membrane, the endolysin can reach the periplasm and break down the peptidoglycan layer. The endolysin is cytoplasmic, but can reach the periplasmic space with the help of the holins which disrupt the host cell membrane.