Alternative splice forms of SMAD5.

(A) SMAD5 and SMAD5β diverge at the junction of exon 6. Arrows denote the exon 6/exon 7 junction of SMAD5 or the exon6/intron 6 junction of SMAD5β. The 5′ splice site (GT) is given in bold. SMAD5β is transcribed through exon 6 and part of intron 6 to terminate at an alternative poly-A site, which is underlined. The novel 18 amino acids are given in bold. Note that codon 334, indicated with triangles, is a glycine (Gly) in both isoforms. The common nucleotide polymorphism and the corresponding amino acid polymorphism are italicized. (B) Comparison of the open reading frames (ORFs) of both isoforms. Schematic depicts the full-length ORFs of SMAD5 (top), which encode 465 amino acids, and the C-terminally truncated splice form SMAD5β (bottom), which encodes 351 amino acids. Both proteins are translated using the same start site and have an identical amino acid sequence through the end of exon 6 (333 amino acids).