Fig. 7: Schematic of defective minor spliceosome induced SMA-associated phenotypes and competition model of minor intron recognition.

SMN is the upstream gene of SMA; a defective minor spliceosome results in inhibited splicing of minS-I- and minS-SS-containing neural genes, and directly induces SMA-associated phenotypes. Splicing recognition of U12-type or minor sensitive introns (minS-I) are proposed as: (i) only by the minor spliceosome; (ii & iii) 5′SS or 3′SS is competitively recognized by the minor and major spliceosomes; (iv) both SSs are competitively recognized by the two spliceosomes.