Essential nuclear envelope/ER integral membrane protein; role in nuclear envelope fusion during biogenesis of the nuclear pore complex ; Brl1p-Brr6p interaction proposed to drive membrane fusion by forming a channel across the bilayers enabling lipid exchange; interacts and functions with Apq12p and Brr6p in lipid homeostasis; identified as a dosage suppressor of a conditional mutation in the major karyopherin, CRM1; Brr6p homolog; functional homolog of metazoan CLCC1