Journal of Molecular Evolution

, Volume 47, Issue 4, pp 378–384

Directionally Evolving Genetic Code: The UGA Codon from Stop to Tryptophan in Mitochondria

  • Yuji  Inagaki
  • Megumi  Ehara
  • Kazuo I.  Watanabe
  • Yasuko  Hayashi-Ishimaru
  • Takeshi  Ohama

DOI: 10.1007/PL00006395

Cite this article as:
Inagaki, Y., Ehara, M., Watanabe, K. et al. J Mol Evol (1998) 47: 378. doi:10.1007/PL00006395

Abstract.

For the comprehensive analyses of deviant codes in protistan mitochondria (mt), we sequenced about a 1.1-kb region of a mitochondrial (mt) gene, the cytochrome c oxidase subunit I (coxI) in two chlorarachniophytes, the filose amoeba Euglypha rotunda, the cryptomonad Cryptomonas ovata, the prymnesiophyte (haptophyte) Diacronema vlkianum (Pavlovales), and the diatom Melosira ambigua. As a result of this analysis, we noticed that the UGA codon is assigned to tryptophan (Trp) instead of being a signal for translational termination in two chlorarachniophytes and in E. rotunda. The same type of deviant code was reported previously in animals, fungi, ciliates, kinetoplastids, Chondrus crispus (a red alga), Acanthamoeba castellanii (an amoeboid protozoon), and three of the four prymnesiophyte orders with the exception of the Pavlovales. A phylogenetic analysis based on the COXI sequences of 56 eukaryotes indicated that the organisms bearing the modified code, UGA for Trp, are not monophyletic. Based on these studies, we propose that the ancestral mitochondrion was bearing the universal genetic code and subsequently reassigned the codon to Trp independently, at least in the lineage of ciliates, kinetoplastids, rhodophytes, prymnesiophytes, and fungi. We also discuss how this codon was directionally captured by Trp tRNA.

Key words: COXI phylogenetic tree — UGA codon — Deviant genetic code — Directional codon reassignment 

Copyright information

© Springer-Verlag New York Inc. 1998

Authors and Affiliations

  • Yuji  Inagaki
    • 1
  • Megumi  Ehara
    • 2
  • Kazuo I.  Watanabe
    • 2
  • Yasuko  Hayashi-Ishimaru
    • 1
  • Takeshi  Ohama
    • 1
  1. 1.JT Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka 569-1125, JapanJP
  2. 2.Department of Biology, Faculty of Science, Osaka University, Machikaneyama-cho, Toyonaka, Osaka 560-0043, JapanJP