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Many labs have been working toward developing that picture, but the task has proven challenging. That's because the enzyme tends to clump together once outside of cells, preventing it from forming the ordered crystals necessary for structural studies. Scientists from Cech's lab and others had tried to simplify matters by crystallizing a portion of the protein, but the segments that they selected clumped together just as stubbornly as the whole enzyme.

Jacobs, a Damon Runyon Cancer Research Foundation fellow in Cech's lab and the first author of the paper, developed a new approach. With the help of bacteria and a protein that emits green fluorescent light, Jacobs randomly screened tens of thousands of fragments of the enzyme for one that would lend itself to successful structural analysis. His strategy took advantage of the fact that when multiple copies of the fluorescent protein clump together, the fluorescence is quenched, or extinguished. So Jacobs engineered bacteria to produce fragments of the telomerase enzyme fused to the fluorescent protein. Since telomerase fragments that clustered together would drag along ?and quench ?their associated fluorescent protein, Jacobs knew that any bright green bacterial colonies were producing protein fragments that remained free. Those rare colonies would be the best candidates for further analysis.

Jacobs performed these experiments on fragments of the telomerase enzyme from a variety of organisms, and found that only a fragment from Tetrahymena -- the single-celled organism in which telomerase was first discovered -- would work. The researchers named the protein fragment "telomerase essential N-terminal" (TEN) domain, in reference to its position within the complete enzyme. It took a few more biochemical tricks, but eventually Jacobs crystallized the protein fragmen
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Source:Howard Hughes Medical Institute