Molecular Info®

Molecular Info® Copy Right © 2001 Institute of Molecular Development LLC

Pyrrolysine Encoded by UAG in Archaea: Charging of a UAG-Decoding Specialized tRNA Gayathri Srinivasan, Carey M. James, Joseph A. Krzycki The Science, May 2002, 294: 1459-1462. Pyrrolysine is a lysine derivative encoded by the UAG codon in methylamine methyltransferase genes of Methanosarcina barkeri. Near a methyltransferase gene cluster is the pylT gene, which encodes an unusual transfer RNA (tRNA) with a CUA anticodon. The adjacent pylS gene encodes a class II aminoacyl-tRNA synthetase that charges the pylT-derived tRNA with lysine but is not closely related to known lysyl-tRNA synthetases. Homologs of pylS and pylT are found in a Gram-positive bacterium. Charging a tRNACUA with lysine is a likely first step in translating UAG amber codons as pyrrolysine in certain methanogens. This results indicate that pyrrolysine is the 22nd genetically encoded natural amino acid.