We have cloned a human cDNA encoding an isoform of the peroxin Pex11p, termed Pex11pgamma, by BLASTP homology search on eukaryotic protein database and reverse transcription (RT)-PCR of human fibroblast RNA. Pex11pgamma was 241 amino-acid long, with two putative transmembrane segments, showing 22% and 23% amino-acid identity to Pex11palpha and Pex11pbeta, respectively. PEX11gamma gene was located on chromosome 19, distinct from PEX11alpha and PEX11beta. Pex11pgamma was found to be a peroxisomal membrane protein, as assessed by colocalization with peroxisome targeting signal type 1 (PTS1)-proteins, in epitope-tagged Pex11pgamma-expressing Chinese hamster ovary cells. Pex11pgamma exposes both of the N- and C-terminal parts to the cytosol. PEX11beta was not induced in rats by treatment of clofibrate, a peroxisome proliferator, similar to constitutively expressed PEX11beta but in contrast to inducible PEX11alpha. (C) 2002 Elsevier Science (USA). All rights reserved.