tRNAPyl: Structure, function, and applications.

Pyrrolysine is the 22nd proteinogenic amino acid encoded into proteins in response to amber (TAG) codons in a small number of archaea and bacteria. The incorporation of pyrrolysine is facilitated by a specialized aminoacyl-tRNA synthetase (PylRS) and its cognate tRNA (tRNAPyl). The secondary structure of tRNAPyl contains several unique features not found in canonical tRNAs. Numerous studies have demonstrated that the PylRS/tRNAPyl pair from archaea is orthogonal in E. coli and eukaryotic hosts, which has led to the widespread use of this pair for the genetic incorporation of non-canonical amino acids. In this brief review we examine the work that has been done to elucidate the structure of tRNAPyl, its interaction with PylRS, and survey recent progress on the use of tRNAPyl as a tool for genetic code expansion.