Sex lethal and U2 small nuclear ribonucleoprotein auxiliary factor (U2AF⁶⁵) recognize polypyrimidine tracts using multiple modes of binding

Site-specific cross-linking of U2AF⁶⁵ to 5-IU containing tra NSS (A), AdML (B), and tra FS (C) Py tracts. The 5-IU RNAs were cross-linked to U2AF⁶⁵(1W23) (lane a′) and U2AF⁶⁵(12W3) (lane b′). Positions of various fragments are indicated; an asterisk represents positions of variant size band(s), which is prominent in lane 8a′, of unknown identity. For reference, the tra (FS) Py-tract sequence is shown in panel C. For further details, see legend to Figure 2.