"This basically demonstrates how something that 'lives' inside the cell can acquire this new functionality and get moved out into the bloodstream to do something else," Cheng said.
Further analysis revealed that the SAS proteins function as enzymes but also have modest ice-binding capabilities. This finding supports a decades-old hypothesis that states that when a single gene begins to develop more than one function, duplication of that gene could result in the divergent evolution of the original gene and its duplicate.
The new finding also supports the proposed mechanism, called "escape from adaptive conflict," by which this can occur. According to this idea, if a gene has more than one function, mutations or other changes to the gene through natural selection that enhance one function may undermine its other function.
"The original enzyme function and the emerging ice-binding function of the ancestral SAS molecule might conflict with each other," Cheng said. When the SAS-B gene became duplicated as a result of a copying error or some other random event in the cell, she said, then each of the duplicate genes was freed from the conflict and "could go on its own evolutionary path."
"This is the first clear demonstration with strong supporting molecular and functional evidence of escape from adaptive conflict as the underlying process of gene duplication and the creation of a completely new function in one of the daughter copies," Cheng said. "This has not been documented before in the field of molecular evolution."
Cheng said that even before the gene for the secreted antifreeze protein was formed, the original SAS protein appears to have had both the enzymatic and
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign