The study identifies a conserved tripeptide (serine-lysine-leucine) at the COOH terminus of proteins as the minimal and sufficient targeting signal for peroxisomal import. This signal is found in many peroxisomal proteins, suggesting it may be a general feature of peroxisomal protein sorting. The tripeptide can be replaced by conservative amino acid substitutions, indicating its structural requirements. The presence of this signal is crucial for protein targeting to peroxisomes, as demonstrated by the inability of mutants lacking it to be imported into peroxisomes. The unique properties of peroxisomal protein import, such as the lack of sequence conservation and the absence of proteolytic modification, suggest that it may involve a different mechanism compared to other types of transmembrane translocation.The study identifies a conserved tripeptide (serine-lysine-leucine) at the COOH terminus of proteins as the minimal and sufficient targeting signal for peroxisomal import. This signal is found in many peroxisomal proteins, suggesting it may be a general feature of peroxisomal protein sorting. The tripeptide can be replaced by conservative amino acid substitutions, indicating its structural requirements. The presence of this signal is crucial for protein targeting to peroxisomes, as demonstrated by the inability of mutants lacking it to be imported into peroxisomes. The unique properties of peroxisomal protein import, such as the lack of sequence conservation and the absence of proteolytic modification, suggest that it may involve a different mechanism compared to other types of transmembrane translocation.