Polyglutamylase which modifies tubulin, generating polyglutamate side chains on the gamma-carboxyl group of specific glutamate residues within the C-terminal tail of tubulin. Preferentially mediates ATP-dependent initiation step of the polyglutamylation reaction over the elongation step. Preferentially modifies the alpha-tubulin tail over a beta-tail (By similarity). Required for CCSAP localization to both polyglutamylated spindle and cilia microtubules (PubMed:22493317). Increases the effects of transcriptional coactivator NCOA2/TIF2 in glucocorticoid receptor-mediated repression and induction and in androgen receptor-mediated induction (PubMed:17116691).
