Figure 1. This coomassie-stained SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) gel shows the proteins present in each successive 0.5-mL fraction of a 15–30% glycerol gradient after centrifugation of a nuclear sonicate containing 40S heterogeneous nuclear ribonucleoprotein (hnRNP) monoparticles. The top of the gradient is to the left. The protein bands labelled near the middle of the gradient are termed the ‘core particle’ proteins. This stoichiometric grouping of major proteins is dissociated from the packaged pre-messenger RNA (pre-mRNA) fragment (approximately 700 nucleotides in length) by the SDS present in the electrophoresis sample buffer. The fast-sedimenting proteins labelled with the asterisk overlap the position of the core particle but are not exclusively enriched in hnRNP complexes.

Figure 2. As in Figure 1, panels (a) and (b) show the distribution of the core particle proteins in 15–30% glycerol gradients; however, in these experiments the spin time was reduced to emphasize the presence of large polyparticle complexes in preparations where nuclease activity is inhibited (a). The electron micrograph insets in (a) reveal 20-nm monoparticles near the top of the gradient, dimers and trimers near the midpoint of the gradient, and polyparticle complexes in fast-sedimenting fractions near the bottom. The solid tracings reveal the distribution of RNA (OD₂₆₀ material) in the gradients.