The Neurospora crassa arg‑2 gene encodes a key enzyme in arginine biosynthesis and is regulated translationally by an upstream open reading frame encoding the arginine attenuator peptide (AAP). In response to high arginine levels, synthesis of the evolutionarily conserved AAP causes ribosome stalling, thereby reducing downstream translation. This study demonstrates that AAP function depends on its amino acid sequence rather than its nucleotide sequence and that it can regulate translation when positioned either upstream or within a larger polypeptide. Mutational and deletion analyses identified a minimal conserved domain required for arginine‑specific regulation. Together, these findings establish the AAP as a conserved peptide domain capable of controlling translational elongation in response to metabolite levels.
