Differences in in vivo acceptor specificity of two galactosyltransferases, the gmh3+ and gma12+ gene products from Schizosaccharomyces pombe.
In the fission yeast Schizosaccharomyces pombe, gmh1+, gmh2+ and gmh3+ genes encode alpha-1,2-galactosyltransferase homologues. In an in vitro galactosyltransferase assay, the gmh3+ gene product showed galactose transfer activity toward a-methyl-D-mannoside as an acceptor. The disruption of gma12+, the major galactosyltransferase gene [Chappell, T. G., Hajibagheri, M. A. N., Ayscough, K., Pierce, M. & Warren, G. (1994) Mol. Biol. Cell 5, 519-528], and of gmh3+ in S. pombe caused decreases in the total remaining galactosyltransferase activity and cell surface galactose content. Disruption of gma12+ and gmh3+ also caused an increase in electrophoretic mobility of acid phosphatase, indicating their involvement in the galactosylation of cell surface glycoproteins. The gmh3delta gma12delta double mutant cells had more severe galactose-less phenotypes than single gene mutant cells. HPLC analysis of O-linked mannoprotein oligosaccharides from wild-type and disrupted strains revealed that the gma12+ gene product is responsible for the galactosylation of O-linked oligosaccharide, whereas gmh3+ has no involvement in the process. In contrast, both the gmh3+ and gma12+ gene products are involved in the galactosylation of the N-linked core oligosaccharide Man9GlcNAc2. From these results, it is evident that there are some functional differences between the enzymes in the process of galactosylation. It appears that the gmh3+ gene product transfers galactose to N-linked oligosaccharide, while the gma12+ gene product transfers galactose to both N-linked and O-linked oligosaccharides.
Yoko-o
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National Institute of Bioscience and Human Technology, Tsukuba, Ibaraki, Japan.
Roy
S K
SK
Jigami
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Y
D001483:Base Sequence; D017931:DNA Primers; D005690:Galactose / Q000378:metabolism; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D007700:Kinetics; D010641:Phenotype; D012568:Schizosaccharomyces / Q000201:enzymology*; D013379:Substrate Specificity
D017931:DNA Primers; D005700:Galactosyltransferases; D005690:Galactose