Gene sharing




 * This article is about genes sharing multiple functions in an organism; for "gene sharing" between organisms, see horizontal gene transfer.

Gene sharing is when a single polypeptide sequence, encoded by a single gene, performs multiple distinct functions in different biological contexts. The most well-studied examples of gene sharing are crystallins. These proteins, when expressed at low levels in many tissues function as enzymes, but when expressed at high levels in eye tissue, become densely packed and thus form lenses. While the recognition of gene sharing is relatively recent&mdash;the term was coined in 1988, after crystallins in chickens and ducks were found to be identical to separately identified enzymes&mdash;recent studies have found many examples throughout the living world. Joram Piatigorsky has suggested that many or all proteins exhibit gene sharing to some extent, and that gene sharing is a key aspect of molecular evolution.

Relationship to similar concepts
Gene sharing is related to, but distinct from, several concepts in genetics, evolution, and molecular biology. Gene sharing entails multiple effects from the same gene, but unlike pleiotropy, it necessarily involves separate functions at the molecular level. A gene could exhibit pleiotropy when single enzyme function affects multiple phenotypic traits; mutations of a shared gene could potentially affect only a single trait. Gene duplication followed by differential mutation is another phenomenon thought to be a key element in the evolution of protein function, but in gene sharing, there is no divergence of gene sequence when proteins take on new functions; the single polypeptide takes on new roles while retaining old ones. Alternative splicing can result in the production of multiple polypeptides (with multiple functions) from a single gene, but by definition, gene sharing involves multiple functions of a single polypeptide.