The function of Ensembl gene identifier ENSG00000213471 (TTLL13, tubulin tyrosine ligase like 13) is as follows. Polyglutamylase which modifies tubulin, generating polyglutamate side chains of variable lengths on the gamma-carboxyl group of specific glutamate residues within the C-terminal tail of tubulin (PubMed:40593606). Mediates ATP-dependent polyglutamate side- chain elongation of the polyglutamylation reaction but not the initiation step (By similarity). Preferentially modifies the alpha- tubulin tail over a beta-tail (By similarity). Mediates spindle-pole microtubule glutamylation in a CFAP100-dependent manner, a modification necessary for maintaining spindle-pole integrity and ensuring proper spindle assembly (PubMed:40593606). {ECO:0000250|UniProtKB:A4Q9F6, ECO:0000269|PubMed:40593606}.