Fig. 5.

Schematic illustration (not drawn to scale) of cryptic out-of-frame translational initiation of mutant (deletion of nucleotides 66–67) TBCE. M1, authentic initiator methionine codon leading to translation of the wild-type sequence. M3′, M12′, and M15′ denote three AUG codons in the −2 reading frame (see Fig. 3A), each of which serves to initiate translation of the mutant allele. Note the transition of all three out-of-frame nonsense translation products (shown as jagged lines) to the correct ORF at the point of mutation (marked by a triangle). Initiation at the authentic M1 AUG codon in the mutant allele leads to translation (not shown) of a peptide consisting of the first 22 aa of TBCE fused to 26 nonsense amino acids translated from the −1 reading frame downstream of the mutation.