This gene encodes a member of glycosyltransferase family 29. The encoded protein is a type II membrane protein that catalyzes the transfer of sialic acid from CMP-sialic acid to galactose-containing substrates. The protein, which is normally found in the Golgi but can be proteolytically processed to a soluble form, is involved in the generation of the cell-surface carbohydrate determinants and differentiation antigens HB-6, CD75, and CD76. This gene has been incorrectly referred to as CD75. Three transcript variants encoding two different isoforms have been described. [provided by RefSeq, Aug 2009],catalytic activity:CMP-N-acetylneuraminate + beta-D-galactosyl-1,4-N-acetyl-beta-D-glucosamine = CMP + alpha-N-acetylneuraminyl-2,6-beta-D-galactosyl-1,4-N-acetyl-beta-D-glucosamine.,function:Transfers sialic acid from the donor of substrate CMP-sialic acid to galactose containing acceptor substrates.,online information:GlycoGene database,online information:ST6Gal I,pathway:Protein modification; protein glycosylation.,PTM:The HB-6, CDW75, and CD76 differentiation antigens are cell-surface carbohydrate determinants generated by this enzyme.,PTM:The soluble form derives from the membrane form by proteolytic processing.,similarity:Belongs to the glycosyltransferase 29 family.,subcellular location:Membrane-bound form in trans cisternae of Golgi. Secreted into the body fluid.,