Phage_holin_2_4 is a family of small hydrophobic phage proteins called holins with one transmembrane domain. Holins are produced by double-stranded DNA bacteriophages that use an endolysin-holin strategy to achieve lysis of their hosts. The endolysins are peptidoglycan-degrading enzymes that are usually accumulated in the cytosol until access to the cell wall substrate is provided by the holin membrane lesion.