Fig. 2. Amino acid sequence of -tubulin and western blot analysis of -tubulin from S100 cell extracts. (A) The amino acid sequence of human -tubulin (TUBA3). Solid boxes indicated the tryptic peptides that were identified by mass spectrometry analysis. Arrows indicate putative grB cleavage sites. (B) HeLa S100 (lanes 1-6) or Jurkat S100 (lanes 7-12) were treated with the indicated amounts of purified grB (in a 10 µl reaction volume), in the presence or absence of 100 µM zVAD-fmk. Protein products were separated by 12% SDS-PAGE and transferred to nitrocellulose. The migration of -tubulin (upper) and caspase 3 (lower) were assessed by western blot analysis. Full-length -tubulin is indicated by ^*, and cleaved -tubulin by ^**. GrB-dependent processing of pro-caspase 3 is indicated by p20, and caspase-dependent processing is indicated by p19.