Fig. 2. Glycerol gradient analysis of OST complexes after siRNA treatment. HeLa cells were mock treated (A) or transfected with siRNAs against ribophorin I (B), STT3A (C) or STT3B (D) and subsequently solubilised in homogenisation buffer containing 1.5% digitonin. The resulting supernatant was loaded onto 8-30% glycerol gradients containing 0.125% digitonin and after centrifugation, thirteen 1-ml fractions were collected and analysed by immunoblotting for the presence of ribophorin I (RibI), OST48, STT3A and STT3B. The data are expressed graphically, and represent the relative band intensity for each component detected following correction of any background. Signals were quantified using Aida software (Fuji), and several different exposures times were used to ensure that the film gave a linear response.