Figure 1.

Ribosomes inhibit glycopeptide export from the ER. Yeast cytosol (18 mg/ml) was separated by centrifugation into ribosomes and a ribosome-free supernatant fraction and the ribosomal pellet resuspended in the original volume B88. Wild-type microsomes [RSY255, 2 μl microsomes (A₂₈₀ = 30) per sample] were translocated with ¹²⁵I-Ac-NYT-NH₂, washed, and incubated for 10 min at 24°C in 12.5 μl B88, 12.5 μl B88 containing nontranslating ribosomes, or 12.5 μl ribosome-free cytosol, as indicated. Glycopeptide export was assayed subsequently for 30 min at 24°C in the absence (−cytosol) or presence (all others) of cytosol and ATP, as described in Methods. Samples contained 2–5 × 10⁴ Con A precipitable cpm, were done in duplicate, and the experiment was repeated three times.