Disrupts the host outer membrane and participates in cell lysis during virus exit (PubMed:30135120). The spanin complex conducts the final step in host lysis by disrupting the outer membrane after holin and endolysin action have permeabilized the inner membrane and degraded the host peptidoglycans (PubMed:30135120). Host outer membrane disruption is possibly due to local fusion between the inner and outer membrane performed by the spanin (PubMed:30135120). Seems to have a dominant negative lysis delay effect on gp11 function. May serve as an intrinsic anti-spanin, providing another level of regulation for u-spanin function. Inserted simultaneously in the host inner membrane and lipid-anchored in the host outer membrane, thereby spaning the whole periplasmic space. The initiator methionine is coded by a non-canonical GTG valine codon. The initiator methionine is coded by a non-canonical GTG valine codon.