ER membrane floppase required for the translocation of Man5GlcNac2-PP-Dol; catalyzes the translocation of the lipid-linked oligosaccharide Man5GlcNac2-PP-Dol across the ER lipid bilayer from the cytoplasmic face to the lumen; mutation is suppressed by expression of human p53 protein; human ortholog RFT1 complements the yeast null mutant