Beta-galactoside alpha-2,6-sialyltransferase 1, also known as B-cell antigen CD75, Sialyltransferase 1, CMP-N-acetylneuraminate-beta-galactosamide-alpha-2,6-sialyltransferase 1, ST6GAL1 and SIAT1, is a single-pass type II membrane protein that belongs to the glycosyltransferase 29 family. Sialyltransferases are key enzymes in the biosynthesis of sialoglycoconjugates that catalyze the transfer of sialic residue from its activated form to an oligosaccharidic acceptor. ST6GAL1 / SIAT1 is normally found in the Golgi but can be proteolytically processed to a soluble form. It is involved in the generation of the cell-surface carbohydrate determinants and differentiation antigens HB-6, CDw75, and CD76. β-Galactoside α2,6-sialyltransferases ST6GAL1 and ST6GAL2 are the two unique members of the ST6GAL family described in higher vertebrates. ST6GAL1 / SIAT1 transfers sialic acid from the donor of substrate CMP-sialic acid to galactose containing acceptor substrates.