Is there a twenty third amino acid in the genetic code?

Authors

Alexey V. Lobanov, University of Nebraska-Lincoln
Gregory V. Kryukov, University of Nebraska-Lincoln
Dolph L. Hatfield, National Institutes of Health, Bethesda, MDFollow
Vadim Gladyshev, University of Nebraska-LincolnFollow

Date of this Version

July 2006

Comments

Published in TRENDS in Genetics - Vol.22 - No.7 - July 2006. Copyright 2006. Permission to use. www.sciencedirect.com.

Abstract

The universal genetic code includes 20 common amino acids. In addition, selenocysteine (Sec) and pyrrolysine (Pyl), known as the twenty first and twenty second amino acids, are encoded by UGA and UAG, respectively, which are the codons that usually function as stop signals. The discovery of Sec and Pyl suggested that the genetic code could be further expanded by reprogramming stop codons. To search for the putative twenty third amino acid, we employed various tRNA identification programs that scanned 16 archaeal and 130 bacterial genomes for tRNAs with anticodons corresponding to the three stop signals. Our data suggest that the occurrence of additional amino acids that are widely distributed and genetically encoded is unlikely.