Transfers sialic acid from CMP-sialic acid to galactose-containing acceptor substrates. a beta-D-galactoside + CMP-N-acetyl-beta-neuraminate = an N-acetyl-alpha-neuraminyl-(2->6)-beta-D-galactosyl derivative + CMP + H(+) kcat is 35.6 min(-1) for the donor CMP-Neu5Ac (at pH 6.5 and 37 degrees Celsius). kcat is 40.3 min(-1) for the acceptor beta-Gal1,4-GlcNAc (at pH 6.5 and 37 degrees Celsius). Protein modification; protein glycosylation. Homodimer (By similarity). Monomer in its soluble form (PubMed:11278697). Membrane-bound form in trans cisternae of Golgi. Secreted into the body fluid. Expressed in hepatocytes (at protein level) (PubMed:3121604, PubMed:11278697). Strongly expressed in liver, spleen, lung, kidney and submaxillary gland and weakly in heart and brain (PubMed:1733948, PubMed:2793863). Expressed in liver. Expressed in kidney, but not in liver. Expressed in kidney, but not in liver. The soluble form derives from the membrane form by proteolytic processing. N-glycosylated. Produced by alternative promoter usage. The alternative promoter is active in kidney. Produced by alternative splicing of isoform RKA. Belongs to the glycosyltransferase 29 family.