Biosynthesis of asparagine-linked oligosaccharides in Saccharomyces cerevisiae: the alg2 mutation

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Abstract
In the yeast Saccharomyces cerevisiae, the alg2 mutation causes temperature-sensitive growth and abnormal accumulation of the lipid-linked oligosaccharide Man2GlcNAc2-PP-Dol (Jackson et al., Arch. Biochem. Biophys., 272, 203–209, 1989; Huffaker and Robbins, Proc. Natl. Acad. Sci. USA, 80, 7466–7470, 1983). A gene having the function and genomic location of ALG2 was cloned from libraries based on the multicopy plasmid YEp24 and on the centromere plasmid YCp50. Alg2 mutants transformed with plasmids containing ALG2 regained the capacity to grow and to synthesize lipid-linked oligosaccharides normally at the previously non-permissive temperature. ALG2 was essential for viability in haploid and diploid yeast. The ALG2 gene was transcribed into a single mRNA of 1.7 kb in size. The stability of ALG2 mRNA, assessed after thermal inactivation of RNA polymerase II in an rpb1–1 mutant (Herrick et al., Mol. Cell. Biol., 10, 2269–2284, 1990) was very low, with a t1/2 of alg2 mutants suggested that the conversion of Man2GlcNAc2-PP-Dol to Man3GlcNAc2-PP-Dol, which is ALG2-dependent, results most likely in formation of the 1→3 branch of the core that is elongated during outer chain formation (Ballou et al., Proc. Natl. Acad. Sci. USA, 87, 3368–3372, 1990; Ballou et al., Proc. Natl. Acad. Sci. USA, 83, 3081–3085, 1986).

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