Holin

Part of speech: noun

Definitions

1. A protein produced by bacteriophages that forms holes in the inner membrane of a bacterial cell so the virus can escape
2. A viral protein that creates pores in the bacterial cell membrane, allowing the newly made phage particles to be released
3. A small membrane protein encoded by bacteriophages that punctures the host cell wall at the right moment to trigger lysis

Etymology: Holin is a modern technical coinage from molecular biology, not an old word with a long history. It names a protein that bacteriophages (viruses that infect bacteria) use to finish their life cycle. When a new virus particle is ready, the holin builds small pores in the bacterial cell's inner membrane at a precisely timed moment. The name is built to pair with "lysin," the term for the enzymes that break down the cell wall. The holin opens the membrane, and the lysin, which had been waiting in the cytoplasm, can then reach the cell wall and dissolve it. The bacterium bursts and releases its new viruses, and the two proteins are named for their complementary jobs in that sequence.