THE HANSENULA-POLYMORPHA PER3 GENE IS ESSENTIAL FOR THE IMPORT OF PTS1 PROTEINS INTO THE PEROXISOMAL MATRIX

PER genes are essential for the assembly of peroxisomes in Hansenula p olymorpha. Here we describe the PER3 gene which was cloned by function al complementation of a H. polymorpha per3 mutant. The complementing P ER3 gene encodes a protein of 569 amino acids (Per3p) with a calculate d mass of 63.9 kDa; Per3p belongs to the tetratricopeptide repeat prot ein family and is located in both the cytosol and the peroxisomal matr ix. Remarkably, Per3p does not contain a known targeting signal (PTS1 or PTS2). The PER3 gene product shows similarity to the Saccharomyces cerevisiae Pas10p (40% identity) and the Pichia pastoris Pas8p (55% id entity). However, their function apparently cannot be interchanged sin ce the P. pastoris PAS8 gene failed to functionally complement a H. po lymorpha per3 disruption mutant, The per3 disruption mutant contained normal but small peroxisomes in which PTS2 proteins (both homologous a nd heterologous) were imported. Other matrix proteins (in particular P TS1 proteins) resided in the cytosol where they were normally assemble d and active. We argue that Per3p is a component of the peroxisomal im port machinery and most probably shuttles matrix proteins from the cyt osol to the organellar matrix.