for National Geographic News
The strength and elasticity of spider silk makes it the toughest natural fiber. Its characteristics could have applications in areas ranging from medicine to ballistics.
Yet only a fraction of the known silk types have been identified at the molecular level. Most of the research has focused on a type of silk known as dragline, which spiders use to construct the frame of their web.
But now scientists have identified the gene for the main protein that female spiders use to make their silken egg cases. The finding could help engineers in their quest to develop applications using artificial spider silk.
"It's likely that the egg case spider silk will have properties that are unique to it because of its specific function," said Jessica Garb, a post doctoral researcher at the University of California, Riverside.
The findings, which also shed light on the evolution of spiders, are reported this week in the journal Proceedings of the National Academies of Science.
There are more than 37,000 known spider species, and probably thousands more that have not been described.
Spiders use silk to move, trap, and store food and to reproduce. Different proteins are made and mixed in silk glands, creating a silk suited to each task.
All spiders have silk genes, which provide the biological instructions for making different proteins. Yet scientists have only identified a few of the silk genes from a small number of species.
Garb and Cheryl Hayashi, a UC Riverside biology professor, isolated a protein called TuSp1 used by 12 types of orb-weaving spiders to make egg case silk.
The egg case silk was shown to be composed of nearly identical, repeating sequences. These gene repeats also share strong similarities across spider species that diverged more than 125 million years ago. The findings point to what is known as concerted evolution among these genes.
"The different elements of a gene sequence typically evolve independently of each other," Garb said. "What happens with concerted evolution is that different segments within the same gene are all evolving together, creating a repetitive sequence."
SOURCES AND RELATED WEB SITES