Essential nuclear envelope integral membrane protein; interacts and functions with Apq12p and Brl1p in lipid homeostasis; role in nuclear envelope fusion during nuclear pore complex biogenesis; interacts with chromatin to help maintain architecture and transcriptional regulation at the nuclear envelope; mutants are defective in NPC biogenesis, nuclear envelope morphology, mRNA nuclear export, and are sensitive to sterol biosynthesis inhibitors and membrane fluidizing agents; homologous to Brl1p