Probable chaperone required for the generation of 1 O-glycan Gal-beta1-3GalNAc-alpha1-Ser/Thr (T antigen), which is a precursor for many extended O-glycans in glycoproteins. Probably acts as a specific molecular chaperone assisting the folding/stability of core 1 beta-3-galactosyltransferase (C1GALT1) (By similarity). Associates with core 1 beta-3-galactosyltransferase (C1GALT1), probably not with the soluble active form. Belongs to the glycosyltransferase 31 family. Beta3-Gal-T subfamily.