Required to generate and maintain the structure of the tubular endoplasmic reticulum network and the vacuole. Induces high curvature in membranes and causes membrane tubule formation. Involved in membrane/vesicle trafficking. Oligomer. The short lumenal loops between transmembrane domains 1 and 2 and between transmembrane domains 3 and 4 may impart a wedge-like configuration, thus deforming membranes. Belongs to the DP1 family.