Figure 3.

Experimental validation of a tandem donor activated in E15 of the SFRS16 gene using RT-PCR and direct sequencing. The top shows the gene structure of SFRS16; in the middle and bottom, E14-16 are schematically extracted and the 3'-end core and full extension sequence of E15 for proximal (TCA/gtaaga) and distal (AAA/gtcagt) splicing are shown. Prior to reaching the 5'ss of E15, both mRNA isoforms cannot be distinguished and consequently the electropherogram displays, for each position, one nucleotide signal peak above the base line. After the tandem donor site, two nucleotide signals above the base line become visible, indicating the presence of two isoforms.