Antagonistic signals within the COX2 mRNA coding sequence control its translation in Saccharomyces cerevisiae mitochondria

Codons 15–25 inhibit translation independently of COX2 mRNA untranslated sequences. Codons 15–25 were introduced with the ARG8^m reporter at the COX3 locus. cox3Δ::ARG8^m completely replaces COX3 coding sequences with those of ARG8^m; cox3–41 inserts only the COX2 codon 89–91 linker between the initiation codon and the ARG8^m reporter; and cox3–42 is like cox3–41 plus the insertion of COX2 codons 15–25. ARG8^m, COX2 codons, and deleted regions are diagrammed as in Figure 1. Suppression of translational inhibition by codons 15–25 at COX3 was assayed in strains overexpressing TIF3 or MRS2 (“+TIF3” and “+MRS2”) compared to a strain transformed with empty vector alone (“+YEp351”). Suppression of translational inhibition at the COX3 locus also was assayed by introduction of the full COX2 leader peptide (“+2–14”), of much of the positive element within codons 2–6 (“+2–6”; Bonnefoy et al. 2001), or of five altered codons (“+2–6*”; Bonnefoy et al. 2001). Strains shown, from top to bottom: EHW334–EHW336 and EHW391–EHW393 (Table 1).