FIG. 3.

Dimer formation by oligoribonucleotides. (A and B) Secondary structure model of the K. lactis pseudoknot element (A), with the positions of the mutations introduced to test stem 2 and the CS3 loop (B) highlighted in gray. The first G residue in CS4 (in lowercase) is not present in the WT sequence but was introduced to facilitate efficient transcription by T7 RNA polymerase. (C) The WT and mutated CS3 and CS4 oligoribonucleotides (0.01 pmol each) described in panels A and B, both radioactively labeled, were denatured, renatured, and analyzed by 15% nondenaturing PAGE at 4°C and pH 6.25. Single oligoribonucleotides are indicated by CS3 or CS4 and asterisks below the lanes. Lanes with mixtures of both CS3 and CS4 are labeled by the name (above) and number (below) of the mutations introduced. Note that the mutant CS4-S2.3 oligoribonucleotide migrated slower than the WT CS4, presumably because the mutated (but not the WT) CS4 alone can form a stable dimer. Since it comigrated with the longer CS3, only one band corresponding to the monomer form appears under S2.3 and S2.3+3′.