HOLINS: The Protein Clocks of Bacteriophage Infections

• Published in: Annual review of microbiology Vol. 54; no. 1; pp. 799 - 825
• Main Authors: Wang, Ing-Nang, Smith, David L, Young, Ry
• Format: Journal Article
• Language: English
• Published: Palo Alto, CA 94303-0139 Annual Reviews 01.01.2000; 4139 El Camino Way, P.O. Box 10139 Annual Reviews, Inc; USA
• Subjects: Amino Acid Sequence; Bacteria; Bacterial genetics; Bacteriolysis - physiology; Bacteriophages; Bacteriophages - growth & development; Biological and medical sciences; Biological Clocks; Coliphages - growth & development; endolysin; endolysins; Endopeptidases - metabolism; Fundamental and applied biological sciences. Psychology; Gene expression; Genetic aspects; Infections; lysis; Lysogeny; lytic cycle; Membrane Proteins - metabolism; membranes; Microbiology; Molecular Sequence Data; peptidoglycan; Proteins; Replicative cycle, interference, host-virus relations, pathogenicity, miscellaneous strains; Siphoviridae - growth & development; Viral Proteins - metabolism; Virology; United States; Virus; Holin; Cytolysis; Membrane protein; Gene; Bacteria; Review; Infected cell; Host virus relation; Phage
• ISSN: 0066-4227; 1545-3251
• DOI: 10.1146/annurev.micro.54.1.799

Two proteins, an endolysin and a holin, are essential for host lysis by bacteriophage. Endolysin is the term for muralytic enzymes that degrade the cell wall; endolysins accumulate in the cytosol fully folded during the vegetative cycle. Holins are small membrane proteins that accumulate in the membrane until, at a specific time that is "programmed" into the holin gene, the membrane suddenly becomes permeabilized to the fully folded endolysin. Destruction of the murein and bursting of the cell are immediate sequelae. Holins control the length of the infective cycle for lytic phages and so are subject to intense evolutionary pressure to achieve lysis at an optimal time. Holins are regulated by protein inhibitors of several different kinds. Holins constitute one of the most diverse functional groups, with >100 known or putative holin sequences, which form >30 ortholog groups.