We have previously reported three Caenorhabditis elegans genes (
gly-12,
gly-13 and
gly-14) encoding enzymatically active UDP-GlcNAc:alpha-3-D-mannoside beta1,2-N-acetylglucosaminyltransferase I (GnT I), an enzyme essential for hybrid, paucimannose and complex N-glycan synthesis. We now describe a worm with null mutations in all three GnT I genes,
gly-14 (III);
gly-12 gly13 (X). The triple "knock out" (TKO) worms have a normal phenotype although they do not express GnT I activity and do not synthesize 31 paucimannose, complex and fucosylated oligomannose N-glycans present in the wild type worm. The TKO worm has increased amounts of non-fucosylated oligomannose N-glycan structures, a finding consistent with the site of GnT I action. Five fucosylated oligomannose N-glycan structures were observed in TKO but not wild type worms indicating the presence of unusual GnT I-independent fucosyltransferases. It is concluded that wild type C.elegans, under laboratory conditions, makes a large number of GnT I-dependent N-glycans that are not essential for normal worm development. Survival of the TKO worm may be compromised if the worm is exposed to environmental stress or if one or more other genes are non-functional. The TKO worm may therefore provide a valuable tool for identifying genes that require an active GnT I for optimum function.