- The Pichia pastoris PER6 gene product is a peroxisomal integral membrane protein essential for peroxisome biogenesis and has sequence similarity to the Zellweger syndrome protein PAF-1. Waterham, H.R., de Vries, Y., Russel, K.A., Xie, W., Veenhuis, M., Cregg, J.M. Mol. Cell. Biol. (1996)