Peroxisome Formation Requires the Endoplasmic Reticulum Channel Protein Sec61

In peroxisome formation, models of near-autonomous peroxisome biogenesis with membrane protein integration directly from the cytosol into the peroxisomal membrane are in direct conflict with models whereby peroxisomes bud from the endoplasmic reticulum and receive their membrane proteins through a branch of the secretory pathway. We therefore reinvestigated the role of the Sec61 complex, the protein-conducting channel of the endoplasmic reticulum (ER) in peroxisome formation. We found that depletion or partial inactivation of Sec61 in yeast disables peroxisome formation. The ER entry of the early peroxisomal membrane protein Pex3 engineered with a glycosylation tag is reduced in sec61 mutant cells. Moreover, we were able to reconstitute Pex3 import into ER membranes in vitro, and we identified a variant of a signal anchor sequence for ER translocation at the Pex3 N-terminus. Our findings are consistent with a Sec61 requirement for peroxisome formation and a fundamental role of the ER in peroxisome biogenesis.