Peroxisomal targeting of mammalian hydroxyacid oxidase 1 requires the C-terminal tripeptide SKI

Peroxisomal proteins are post-translationally imported into peroxisomes aft er recognition by specific receptors, Tbe best-defined peroxisomal targetin g signal is a C-terminal tripeptide SKL. Different functional variants of t his tripeptide have been defined, but mutants with a SKI sequence were reco gnized as being inefficiently targeted to peroxisomes. Recently, we have cl oned a cDNA for the mouse hydroxyacid oxidase 1 (Hao1), a protein that seem s to be localized in peroxisomes. Interestingly, the mouse Hao1 sequence co mprises a C-terminal SKI tripeptide, We have analyzed the subcellular local ization off Hao1 and tested whether its SKI sequence acts as a targeting si gnal. Ltk(-) and Cos-7 cells were transfected with vectors expressing a fus ion protein of green fluorescence protein and Hao1, as well as mutants ther eof. Targeting to peroxisomes of the fusion protein with the wild-type SKI sequence was highly selective and as complete as with the peroxisome-specif ic SKL sequence, By contrast, targeting was lost in a mutant with the seque nce CKM, The data show that mammalian Hao1 is a peroxisomal protein and tha t the C-terminal sequence SKI acts as the targeting signal.