Figure 4. Deletion of the SMN C-terminus affects calpain cleavage.

(A) A representative Western blot (for illustrative purposes only) demonstrating the calpain cleavage susceptibility of several C-terminal mutants. (B) Quantification of GFP-SMN cleavage was determined from Western blots probed with N-terminal SMN antibodies followed by Cy3 conjugated secondary antibodies (see Methods). The average fraction (expressed as %) of calpain cleavage was calculated from six independent cell-free cleavage assays. Removal of amino acids 268-294 (ΔYG+) in SMN renders it more susceptible to calpain cleavage, whereas mutations in the YG box or exon 7 (ΔEx7) did not. Error bars represent the SEM. Asterisks (**) indicate p value <0.001, determined by two-tailed Student T-test.