a new amino acid, but the researchers knew there might be other explanations as well. Krzycki and his colleagues sliced the protein into smaller bits called peptides, and began sequencing them, a process which usually ultimately reveal the amino acid responsible for the protein.

"That all seemed to point to this being just lysine, one of the normal amino acids," Chan said. Regardless, Kyzycki asked Chan and Ph.D. student Bing Hao to start working on deducing the crystalline structure of the protein containing the amino acid. At the end of the two-year process, Hao and Chan had determined the structure of the protein, part of which revealed a new amino acid.

At the same time, Krzycki was looking for other evidence. He, along with doctoral students Gayathri Srinivasan and Carey James, was eventually able to identify the specific transfer-RNA (tRNA) needed to insert the new amino acid into protein, as well as another important enzyme essential to the process. These two discoveries, along with the detailed crystalline structure, convinced the teams that they had found a new genetically encoded amino acid -- pyrrolysine - the 22nd known to science.

"We realized that we had to know which tRNA would decode that amber codon," Krzycki said. "Finding it was an essential part of the puzzle."

He believes this will be a very rare amino acid, given the fact that it has taken so long to identify it. However, Krzyck
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Contact: Joseph A. Krzycki
Krzycki.1@osu.edu
614-292-1578
Ohio State University
23-May-2002

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