Enables beta-1,3-galactosyltransferase activity. Involved in protein glycosylation. Located in Golgi medial cisterna. Is expressed in adult head; ejaculatory duct; gland; salivary gland body primordium; and testis. Orthologous to human C1GALT1 (core 1 synthase, glycoprotein-N-acetylgalactosamine 3-beta-galactosyltransferase 1).