Figure 3.

A model for early stages of peroxisomal membrane biogenesis involving mutually dependent targeting of Pex3p and Pex16p, named classes I and II pathways. The initial membranes harboring Pex3p or Pex16p culminate in indistinguishable, matured peroxisomes. Pex19p forms complexes in the cytosol with newly synthesized PMPs including Pex16p and C-tailed anchored membrane proteins such as Pex26p and transports them to the membrane protein receptor Pex3p, whereby peroxisome membrane is assembled (Class I pathway). With respect to biogenesis of Pex3p, Pex19p likewise forms a complex with newly synthesized Pex3p and translocates it to the Pex3p receptor, Pex16p (Class II pathway). Of note, peroxisomes are assembled no matter which pathway initially proceeds.