FUNCTION Catalyzes the formation of the NeuAc-alpha-2,3-Gal-beta-1,4-GlcNAc-, NeuAc-alpha-2,3-Gal-beta-1,3-GlcNAc- and NeuAc-alpha-2,3-Gal-beta-1,3-GalNAc- sequences found in terminal carbohydrate groups of glycoproteins and glycolipids. The highest activity is toward Gal-beta-1,3-GlcNAc and the lowest toward Gal-beta-1,3-GalNAc.CATALYTIC ACTIVITY a beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP-N-acetyl-beta-neuraminate = an N-acetyl-alpha-neuraminyl-(2->3)-beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP + H(+)PATHWAY Protein modification; protein glycosylation.INTERACTION Membrane-bound form in trans cisternae of Golgi. Secreted into the body fluid.ALTERNATIVE PRODUCTS Highly expressed in adult skeletal muscle and in all fetal tissues examined and to a much lesser extent in placenta, lung and liver.PTM The soluble form derives from the membrane form by proteolytic processing.DISEASE The disease is caused by variants affecting the gene represented in this entry.DISEASE The disease is caused by variants affecting the gene represented in this entry.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.MISCELLANEOUS May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.SIMILARITY Belongs to the glycosyltransferase 29 family.ONLINE INFORMATION ST3Gal III