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Happy accident

作者:廉胧    发布时间:2019-03-07 06:04:12    

By Jonathan Knight A GENE in an Antarctic fish has turned out to be the missing link that confirms that the natural antifreeze of atlantic cod and related fish evolved from a digestive protein. Certain Antarctic fish have glycoproteins (AFGPs) in their blood that act as a kind of antifreeze, helping them to survive in icy waters. These proteins bind to ice crystals and stop them from growing inside the fish. Parts of three genes that code for AFGPs resemble the gene for an enzyme found in the intestines of the fish, leading researchers to speculate that one evolved from the other. Now Chi-Hing Cheng and Liangbiao Chen at the University of Illinois in Urbana-Champaign have sequenced a fourth AFGP gene from notothenioids, a group of fish sometimes called Antarctic cod. Tacked on at the end of this gene, they discovered an entire copy of a fifth gene. This one codes for an enzyme made in the pancreas, which chews up proteins in the gut (Nature, vol 401, p 443). “We had hypothesised that it could have given rise to antifreeze, but this is living proof,” says Cheng. Because the part of AFGPs that binds to ice relies on a repetition of three amino acids, a “stuttering” or mistake in the machinery that copies DNA could have converted an extra copy of the digestion gene to an ancestral form of AFGP,

 

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