Figure 6.

Molecular frameworks for splicing fidelity. (A) The previously proposed kinetic proofreading model for Prp16p function (Burgess and Guthrie 1993b) is integrated with the two-state model of the spliceosome recently proposed by Query and Konarska (2004). The transition between the first-step (LI)- and second-step (LI*)-specific conformations of the spliceosome is influenced by the Δisy1 and prp16-302 mutants as discussed in the text. (B) Elements of the catalytic core at the time of second-step activation. Nucleotides having genetic interaction with PRP16 are indicated in bold and italicized letters. Black dots represent tertiary interactions. The upstream ACA trinucleotide in U6 is boxed.