Catalysis of the reaction: alpha-N-acetylneuraminyl-(2->3)-beta-D-galactosyl-(1->3)-N-acetyl-D-galactosaminyl-R + CMP-N-acetyl-beta-neuraminate = alpha-N-acetylneuraminyl-(2->3)-beta-D-galactosyl-(1->3)--N-acetyl-D-galactosaminyl-R + CMP.
ST6GALNAC activity