Deletions delineate COX2 coding sequence capable of inhibiting translation of downstream ARG8m in the absence of COX2 codons 2–14. (A) Deletion constructs consist of variable numbers of COX2 codons 15–88 (light gray boxes), COX2 codons 89–91 (gray boxes), and ARG8m (dark gray boxes). Dashed lines represent deleted regions. The growth phenotypes of these strains when streaked on medium lacking arginine are shown, with full prototrophy as “+++.” All strains grow equally well on medium containing arginine (data not shown). Strains shown, from top to bottom: NB43, NB120, and EHW161–EHW154 (Table 1). (B and C) ARG8m, COX2 codons 89–91, and deleted regions are depicted as in A. Cox2p residues coded by each allele within the codon 15–25 region are as written. Strains marked with an asterisk revert to full arginine prototrophy (“+++”) by mutation of a single nucleotide. Strains shown from top to bottom in B: EHW155, EHW195–EHW204, and EHW154; and in C: EHW155, EHW185–EHW194, and EHW154 (Table 1).
