MOLECULAR-CLONING OF SIA-ALPHA-2,3GAL-BETA-1,4GLCNAC ALPHA-2,8-SIALYLTRANSFERASE FROM MOUSE-BRAIN

A cDNA encoding a new alpha 2,8-sialyltransferase (ST8Sia III), which exhibits activity toward the Sia alpha 2,3Gal beta 1, 4GlcNAc sequence s of N-linked oligosaccharides, was cloned from mouse brain by means o f the polymerase chain reaction based approach. The predicted amino ac id sequence of ST8Sia III showed 27.6 and 34.4% identity with those of so far cloned mouse alpha 2,8-sialyltransferases, i.e. G(D3) synthase (ST8Sia I) and STX (ST8Sia II), respectively. Transfection of the pro tein A-fused ST8Sia III gene into COS-7 cells led to alpha 2,8-sialylt ransferase activity toward sialylated glycoproteins and alpha 2,3-sial ylated glycosphingolipids, such as alpha 2,3-sialylparagloboside and G (M3). However, the kinetic properties of ST8Sia III revealed that it i s much more specific to N-linked oligosaccharides of glycoproteins tha n glycosphingolipids. The expression pattern of the ST8Sia III gene wa s clearly different from those of other alpha 2,8-sialyltransferase ge nes. The expression of the ST8Sia III gene was tissue and stage specif ic. The ST8Sia III gene was expressed only in brain and testis, and it appeared first in 20 postcoitum embryonal brain and then decreased. T herefore, the new alpha 2,8-sialyltransferase is closely involved in b rain development.