FIG. 7.

Yeast box C/D and C′/D′ RNPs exhibit a defined range of inter-RNP spatial positioning assisted by spacer region folding. (A) Box C/D and C′/D′ inter-RNP spacing of yeast box C/D snoRNAs. Distances between the C-D′ boxes (black bars) and the C′-D boxes (gray bars) were determined and plotted versus the number of yeast box C/D snoRNAs in the indicated nucleotide spacing range. Regions of each bar represented in white are that fraction of snoRNAs which exhibit potential hairpin structures in their C-D′ or C′-D spacer regions. (B) Yeast box C/D snoRNAs utilizing spacer region folding to facilitate coupling of the box C/D and C′/D′ RNPs. Box C/D and C′/D′ sequences are blocked in black with the D′ guide regions base paired to their complementary sequences in 25S rRNA. Evolutionarily conserved hairpin structures which shorten the inter-RNP distances are indicated.