Transfers sialic acid from the donor of substrate CMP-sialic acid to galactose containing acceptor substrates. Has alpha-2,6-sialyltransferase activity toward oligosaccharides that have the Gal-beta-1,4-GlcNAc sequence at the non-reducing end of their carbohydrate groups, but it has weak or no activities toward glycoproteins and glycolipids. a beta-D-galactoside + CMP-N-acetyl-beta-neuraminate = an N-acetyl-alpha-neuraminyl-(2->6)-beta-D-galactosyl derivative + CMP + H(+) Weakly expressed in some tissues, such as small intestine, colon and fetal brain. By IL6/interleukin-6 and IL8//interleukin-8. O-glycosylated. Belongs to the glycosyltransferase 29 family. Truncated N-terminus. Extended N-terminus.