A) Alignment of sequences of all human α- and β‑tubulin isotypes. Only the C-terminal tail region of the tubulins are shown. Isotypes with identical amino acid sequence in these regions are pooled. A large number of glutamate residues in the C-terminal tails would, if modified by glutamylation, be detectable with GT335 (yellow), which requires one additional acidic amino acid residue after the modification site (Wolff et al, 1992). By contrast, the GEF motif (red/purple), which is the main glutamylation site in β2‑tubulin (TUBB2) in the brain (Rüdiger et al, 1992), is present only in a few β‑tubulin isotypes, but not in α-tubulin. 