Figure 8.

Model for competing U6 intra- and intermolecular interactions involved in U4/U6 unwinding and spliceosome activation. Telestem base-pairing and additional structures formed upon disruption of U4/U6 stem I promote destabilization of stem II by oligonucleotides, resulting in unwinding and formation of the extensively base-paired U6 snRNA. During spliceosome activation, disruption of U4/U6 stem I by the Brr2 helicase may facilitate formation of competing intermolecular base-pairing interactions between U6, U2 and the pre-mRNA. These interactions may similarly promote destabilization of U4/U6 stem II, resulting in concomitant formation of the U2/U6 catalytic core of the spliceosome.