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Protein moonlighting (or gene sharing) is a phenomenon by which a protein can perform more than one function.〔 Ancestral moonlighting proteins originally possessed a single function but through evolution, acquired additional functions. Many proteins that moonlight are enzymes; others are receptors, ion channels or chaperones. The most common primary function of moonlighting proteins is enzymatic catalysis, but these enzymes have acquired secondary non-enzymatic roles. Some examples of functions of moonlighting proteins secondary to catalysis include signal transduction, transcriptional regulation, apoptosis, motility, and structural.〔 Protein moonlighting may occur widely in nature. Protein moonlighting through gene sharing differs from the use of a single gene to generate different proteins by alternative RNA splicing, DNA rearrangement, or post-translational processing. It is also different from multifunctionality of the protein, in which the protein has multiple domains, each serving a different function. Protein moonlighting by gene sharing means that a gene may acquire and maintain a second function without gene duplication and without loss of the primary function. Such genes are under two or more entirely different selective constraints.〔 Various techniques have been used to reveal moonlighting functions in proteins. The detection of a protein in unexpected locations within cells, cell types, or tissues may suggest that a protein has a moonlighting function. Furthermore, sequence or structure homology of a protein may be used to infer both primary function as well as secondary moonlighting functions of a protein. 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—the term was coined in 1988, after crystallins in chickens and ducks were found to be identical to separately identified enzymes—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.〔 The genes encoding crystallins must maintain sequences for catalytic function and transparency maintenance function.〔 Inappropriate moonlighting is a contributing factor in some genetic diseases, and moonlighting provides a possible mechanism by which bacteria may become resistant to antibiotics.〔 == Discovery == The first observation of a moonlighting protein was made in the late 1980s by Joram Piatigorsky and Graeme Wistow during their research on crystallin enzymes. Piatigorsky determined that lens crystallin conservation and variance is due to other moonlighting functions outside of the lens.〔 Originally Piatigorsky called these proteins "gene sharing" proteins, but the colloquial description moonlighting was subsequently applied to proteins by Constance Jeffery in 1999〔 to draw a similarity between multitasking proteins and people who work two jobs.〔 The phrase "gene sharing" is ambiguous since it is also used to describe horizontal gene transfer, hence the phrase "protein moonlighting" has become the preferred description for proteins with more than one function.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「protein moonlighting」の詳細全文を読む スポンサード リンク
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