Catalyzes the reaction that attaches fucose through an O-glycosidic linkage to a conserved serine or threonine residue found in the consensus sequence C2-X(4,5)-[S/T]-C3 of EGF domains, where C2 and C3 are the second and third conserved cysteines. Specifically uses GDP-fucose as donor substrate and proper disulfide pairing of the substrate EGF domains is required for fucose transfer. Plays a crucial role in NOTCH signaling. Initial fucosylation of NOTCH by POFUT1 generates a substrate for FRINGE/RFNG, an acetylglucosaminyltransferase that can then extend the fucosylation on the NOTCH EGF repeats. This extended fucosylation is required for optimal ligand binding and canonical NOTCH signaling induced by DLL1 or JAGGED1. Fucosylates AGRN and determines its ability to cluster acetylcholine receptors (AChRs). GDP-beta-L-fucose + L-seryl-[protein] = 3-O-(alpha-L-fucosyl)-L-seryl-[protein] + GDP + H(+) GDP-beta-L-fucose + L-threonyl-[protein] = 3-O-(alpha-L-fucosyl)-L-threonyl-[protein] + GDP + H(+) Protein modification; protein glycosylation. Increased expression throughout embryo development. Ubiquitous expression at 9.5 dpc and 11.5 dpc with lower expression at 9.5 dpc. N-glycosylated. Early embryos of null mice are defective in somitogenesis. At 8.5 dpc, embryos are of normal size and appearance but somites adjacent to the presomitic mesoderm (PSM) are fused. In 8.25 dpc embryos, expression of NOTCH target genes such as HES5 and JAG1 as well as LFNG and UNCX4.1 is severely reduced in somites. There is up-regulation of a number of these genes such as HES5 and LFNG as well as DLL1 and NOTCH1 in the neural tube and brain. Mice die at midgestation with severe defects in somitogenesis, vasculogenesis, cardiogenesis and neurogenesis. The cax (compact axial skeleton) spontaneous mutation is a hypomorphic allele that reduces Pofut1 expression and protein levels leading to reduced Notch signaling. cax mutant embryos have somites of variable size, partly abnormal Lfng expression, defective anterior-posterior somite patterning and abnormal axial skeleton development. Mice have kinky and shortened tails and shortened body length (PubMed:19161597). Belongs to the glycosyltransferase 65 family. Peptide-O-fucosyltransferase 1