FIG. 1.

Diversity of intronic sequence architectures and requirements for U2AF subunits in splicing. (A) Four categories of S. pombe introns with respect to the length and positions of Py tracts with respect to the BPS: upstream (UY), downstream (DY), both up and downstream (UDY), and none (NY). The circle size corresponds to the relative frequency of each fraction. (B) Introns with variable-length Py tracts between the BPS and the 3′ SS show diverse requirements for U2AF subunits. The splicing patterns were determined using semiquantitative RT-PCR for endogenous introns (indicated on the left) in wild-type (prp2⁺), prp2.1, U2AF²³-ts, and prp10 mutant strains incubated for 0, 1, and 2 h at 37°C. Positions of spliced and unspliced RNAs are indicated on the right. (C) Sequences of the introns used above are shown. The 5′ and 3′ splice sites and the predicted BPS are shown in uppercase letters. The Py tracts in this and subsequent figures are underlined. Intron SPBC27B12. 07_b is abbreviated as SPBC27.