Fig. 1.

Diagram of pre-mRNA splicing steps and trans-acting 3′SS regulators. Shown at the top is splice sites motifs shown in different colors with consensus sequence and represented in the intron with respective colors. 5′SS (maroon line), BP (blue line), Py (green line) and 3′AG (olive line). Below is the stepwise assembly of constitutive splicing factors (ovals) for excision of intron between exon 1 (red) and exon 2 (blue). Boxes on the right list trans-acting alternative splicing factors that regulate the corresponding steps of spliceosome assembly for exon 2 splicing