Fig 1.

Possible mechanisms for Ost1p labeling by the Asn-Bpa-Thr photoprobe. In model I, the probe attachment site (arrow) is postulated to be in close proximity to the N-glycosylation site recognition region (bend) in the primary sequence of Ost1p. In model II, the probe attachment site is not in the vicinity of the glycosylation site recognition region, but is elsewhere in the primary sequence of Ost1p. In model III, it is postulated that the glycosylation site recognition region and/or the catalytic site actually is in another OT subunit, but Ost1p is located in proximity to this other subunit and consequently is labeled by the photoprobe.