Research

Conservation of tandem stop codons in yeasts

Han Liang¹, Andre RO Cavalcanti² and Laura F Landweber^2*

• * Corresponding author: Laura F Landweber lfl@Princeton.edu

Author Affiliations

¹ Department of Chemistry, Princeton University, Princeton, NJ 08544, USA

² Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA

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Genome Biology 2005, 6:R31 doi:10.1186/gb-2005-6-4-r31

Published: 16 March 2005

Abstract

Background

It has been long thought that the stop codon in a gene is followed by another stop codon that acts as a backup if the real one is read through by a near-cognate tRNA. The existence of such 'tandem stop codons', however, remains elusive.

Results

Here we show that a statistical excess of stop codons has evolved at the third codon downstream of the real stop codon UAA in yeasts. Comparative analysis indicates that stop codons at this location are considerably more conserved than sense codons, suggesting that these tandem stop codons are maintained by selection. We evaluated the influence of expression levels of genes and other biological factors on the distribution of tandem stop codons. Our results suggest that expression level is an important factor influencing the presence of tandem stop codons.

Conclusion

Our study demonstrates the existence of tandem stop codons, which represent one of many meaningful genomic features that are driven by relatively weak selective forces.