An internal AUU codon initiates a smaller peptide encoded by bacteriophage T4 baseplate gene 26.

Bacteriophage T4 baseplate gene 26 codes for two in-frame overlapping peptides with identical C-terminal regions. By site-directed mutagenesis we have now determined that an internal AUU, codon 114 of gene 26, is used as the initiation codon for the synthesis of a smaller peptide (gp26*). Thus gene 26* gives rise to a peptide of 95 amino acid residues with an Mr of 10,873, while the complete gene 26 encodes a peptide of 208 amino acid residues of M(r) 23,880. Expression of gene 26* is shown to depend on the RNA secondary structure in the translational initiation region of this gene.