Fig. 6. Effect of OST subunit knockdown on the N-glycosylation of secretory proteins. (A) Yeast prepro factor was synthesised as before to determine the extent of its N-glycosylation (cf. Fig. 3A). The resulting fully glycosylated (+ 3CHO) and non-glycosylated (– CHO) polypeptides are shown. In this case any untranslocated prepro factor where the signal sequence has not been cleaved co-migrates with the translocated signal sequence cleaved form that has not been glycosylated (see products labelled CHO/ppf). This means that the measured proportion of correctly translocated, N-glycosylated, chains is an underestimate of the true value (cf. Fig. 6B). The proportion of N-glycosylated pro factor was calculated as before (Fig. 3A) with symbols as previously defined. (B) Human -interferon was synthesised as in A, four forms of the protein can be resolved, the doubly glycosylated form (+ 2CHO), a singly glycosylated form (+ 1CHO), the non-glycosylated form (– CHO) and an untranslocated form where the pre-sequence has not been cleaved (pIF). Data analysis of -interferon was performed as in A. Numbers below the lanes are the mean ± s.e.m. of three independent experiments. Levels of N-glycosylation that differ from the mock-treated control by a significance of at least 0.02 are indicated (^*).