Peroxisomal integral membrane protein; negative regulator of peroxisome size; partial functional redundancy with Pex30p and Pex32p; may act downstream of Pex28p and Pex29p; involved in metabolic adaptation of the nucleus-vacuole junction (NVJ); enriched at the NVJ in high glucose conditions; PEX31 has a paralog, PEX30, that arose from the whole genome duplication