Figure 4.

Identification of a novel cryptic donor splice site in integrin α7 exon 21. Full length and alternatively spliced integrin α7 are shown. Full length integrin α7 is the major transcript in adult skeletal muscle and results from the expected splicing from exon 21 to exon 22 (wild-type integrin α7 in the figure). The alternatively spliced integrin α7 derives from the use of a cryptic splice site starting at position 2639 (AG/GTTA₂₆₄₄AG) of the integrin cDNA resulting in the skipping of about 40% of the exon 21. PCR/SSCP of exon 21, in the original patient where the alternatively spliced isoform was identified, showed a G to A nucleotide change at position 2644 (bold). Nucleotide sequence 5[prime] of the G2644A nucleotide substitution were consistent with a consensus donor splice site sequence: 2639A⁻²₆₂G⁻¹₇₇/G⁺¹₁₀₀T⁺²₁₀₀T⁺³_xx. The G to A substitution at position + 4 of the intron 21 created a weak donor sequence according to an algorithm to identify splice site based on a Shapiro and Senapathy matrix. In the alternatively spliced integrin α7 the donor splice site sequence is shown. Numbers below each base give the frequency of occurrence. 49