Accumulates harmlessly in the cytoplasmic membrane until it reaches a critical concentration that triggers the formation of micron-scale pores (holes) causing host cell membrane disruption and endolysin escape into the periplasmic space. Determines the precise timing of host cell lysis. Participates with the endolysin protein in the sequential events which lead to the programmed host cell lysis releasing the mature viral particles from the host cell. Homomultimer.