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Figure S4. Cosmc itself does not have any T-synthase activity. 293T cells were transiently transfected with plasmids encoding soluble secreted N-terminal HPC-tagged human T-synthase and soluble secreted N-terminal HPC-tagged Cosmc with or without C-terminal KDEL-tag. At 72 h after transfection, the media were harvested respectively. T-synthase activity in one portion of media was assayed using GalNAc-α-phenyl as an acceptor (A; error bars represent ±1 SD from the mean). The other portions of media were incubated with HPC4-Ultralink beads. After washing, part of the beads was used for T-synthase activity assay (A) and the other part was incubated with the buffer containing 5 mM EDTA to elute the bound proteins. The eluates were analyzed by Western blot (B).