Screening for all feasible non-AUG initiation codons. (A) Nucleotide sequences -250 to +60 relative to ATG1 of ALA1. For clarity, the translation initiation codons ACG(-25)/ACG(-24) and ATG1 are boxed, and the mitochondrial targeting signal is shaded. The amino acid residue encoded by ACG(-25) is labeled M*. The cleavage site for the mitochondrial matrix-processing peptidase is marked under the sequence by a black triangle (▲). (B) Screening for feasible non-AUG initiator codons.