Glycerol gradient fractionation reveals altered snRNP distributions in U6-II extracts. Yeast cell extracts were sedimented through a 10%–30% glycerol gradient, fractionated, and snRNAs analyzed by primer extension. To normalize the data, the U4, U5, and U6 primer extension products in peak tri-snRNP-containing fractions for each gradient (20 or 21) were set to values of “1” since these RNAs are expected to be equimolar in tri-snRNPs. Asterisks denote fractions for which no detectable U4 RNA above background was detected. (A–C) Relative abundances of the U4 (red), U5 (brown), and U6 (blue) RNAs in each glycerol gradient fraction obtained using WT (A), U6-II (B), or U6-II-Sm (C) yeast extract. (D) The normalized U4/U6 ratio is plotted for each fraction from gradients of extracts prepared from WT (blue squares), U6-II (yellow circles), or U6-II-Sm (green triangles) strains.
