Fig 1. Attempts to separate polyribosomes from heavy sedimenting granules.

A) Brain cytoplasmic extract prepared without detergent was analysed by sedimentation velocity throughout a 5–30% (w/v) sucrose density gradient layered over a 70% (w/v) sucrose cushion. The collected fractions were analysed by SDS-PAGE followed by Coomassie blue staining and immunoblotting to detect the ribosomal protein L7 and FMRP. A major UV-absorbing peak is observed at the 30–70% sucrose interface that contained L7 and FMRP. Electron micrographs of this fraction revealed that both beads on a string like structures of polyribosomes and dense amorphous granule-like structures (arrows) were recovered at the interface. B) Total polyribosomes from brain cytoplasmic extract were first concentrated by ultracentrifugation, resuspended, and then analysed by sedimentation velocity throughout a 15–60% (w/v) sucrose density gradient layered over a 70% (w/v) sucrose pad. All collected fractions were analysed by Coomassie blue staining after SDS-PAGE, and by immunoblotting to detect the ribosomal protein L7 and FMRP. While polyribosomes were detected in the middle of the gradient, electron micrographs revealed that the sucrose interface fraction contained 100–800 nm diameter granule-like structures. Note the extended scale in B as compared to that in panel A.