Essential component of glycosylphosphatidylinositol-mannosyltransferase 1 which transfers the first of the 4 mannoses in the GPI-anchor precursors during GPI-anchor biosynthesis. Probably acts by stabilizing the mannosyltransferase PIGM. Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Interacts with PIGM. N-glycosylated. Belongs to the PIGX family. PubMed:15635094 reported that the initiator methionine is coded by an unusual start codon, CTG. Unusual initiator. The initiator methionine is coded by a non-canonical CTG leucine codon.