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). Associates with core 1 beta-3-galactosyltransferase (C1GALT1), probably not with the soluble active form. Ubiquitously expressed. Abundantly expressed in salivary gland, stomach, small intestine, kidney, and testis and at intermediate levels in whole brain, cerebellum, spinal cord, thymus, spleen, trachea, lung, pancreas, ovary, and uterus. The disease is caused by variants affecting the gene represented in this entry. Defects in C1GALT1C1 in Ag104A cell line create a tumor-specific glycopeptidic neo-epitope. This epitope induces a high-affinity, highly specific, syngeneic monoclonal antibody. This is caused by the abolition of function of a glycosyltransferase, disrupting O-glycan Core 1 synthesis. Belongs to the glycosyltransferase 31 family. Beta3-Gal-T subfamily. Was originally (PubMed:12361956) assigned to be a glycosyltransferase. However, it was later shown (Ref.2 and PubMed:12464682) that it has no transferase activity and rather acts as a chaperone. C1GALT1-specific chaperone 1