SRSF3 and SRSF4 contact exons and introns. (a) SRSF3 and SRSF4 crosslink sites mapped around the 5' and 3' splice sites. The position 0 (dotted line) represents the indicated 5' or 3' splice site; the y-axis represents normalized crosslink sites per 103 nucleotides. The normalization is based on the length distribution of exons and introns (Figure S5 in Additional file 1). The data were smoothed using a Gaussian window (half-width of the window = 5). (b) SRSF3 and SRSF4 crosslink sites mapped to predicted mouse branch points. The position 0 (dotted line) represents the branch point nucleotide. Smoothing as in (a).