title: Conservation of tandem stop codons in yeasts.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Chemistry, Princeton University, Princeton, NJ 08544, USA. hliang@Princeton.edu
authors.forename: Han
authors.initials: H
authors.lastname: Liang
authors.forename: Andre R O
authors.initials: AR
authors.lastname: Cavalcanti
authors.forename: Laura F
authors.initials: LF
authors.lastname: Landweber
mesh_terms: D001483:Base Sequence; D018388:Codon, Terminator / Q000235:genetics*; D017124:Conserved Sequence / Q000235:genetics*; D005800:Genes, Fungal; D012641:Selection, Genetic; D015003:Yeasts / Q000235:genetics*
chemical_list: D018388:Codon, Terminator