Glycobiology, 2000, Vol. 10, No. 10 1001-1011
© 2000 Oxford University Press
A novel variant form of murine ß-1,6-N-acetylglucosaminyltransferase forming branches in poly-N-acetyllactosamines
Department of Biochemistry, Nagoya University School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466–8550, Japan
A novel form of murine ß-1,6-N-acetylglucosaminyltransferase that forms branches in poly-N-acetyllactosamines (designated as IGnT B) was cloned based on sequence homology to the known IGnT (designated as IGnT A). When expressed as proteins, IGnT B showed higher specific activity than IGnT A. The C-terminal 1/4 of IGnT B was identical to that of IGnT A, while the rest of the predicted sequences showed 63% identity. Genomic analysis indicated that IGnT A and IGnT B were derived by alternative splicing; the unique portion was encoded by exon 1, and the common portion was encoded by exons 2 and 3. IGnT B showed an expression profile closely related to that of IGnT A and was strongly expressed in the liver, kidney and intestine, and moderately in the mammary gland, submaxially gland, embryonic stem cells, and embryonal carcinoma cells. The specificity of IGnT B examined using various substrates was indistinguishable from that of IGnT A, which is classified as the central acting IGnT (cIGnT). Thus, IGnT B acted on Galß1–4GlcNAcß1–3Galß1–4Glc, but not on GlcNAcß1–3Galß1–4Glc. It formed branches in both of the internal galactosyl residues of Galß1–4Glc-NAcß1–3Galß1–4GlcNAcß1–3Galß1–4Glc, and prolonged incubation resulted in production of the di-branched oligosaccharide. Although addition of sialic acid to the terminal galactosyl residue did not abolish the acceptor activity, 
2–6 sialylation was a preferred one as compared to 2–3 sialylation.
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