Polyglutamylase which modifies both tubulin and non-tubulin proteins, generating alpha-linked polyglutamate side chains on the gamma-carboxyl group of specific glutamate residues of target proteins. Preferentially mediates ATP-dependent long polyglutamate chain elongation over the initiation step of the polyglutamylation reaction. Preferentially modifies the alpha-tubulin tail over a beta-tail. Promotes tubulin polyglutamylation which stimulates spastin/SPAST-mediated microtubule severing, thereby regulating microtubule functions. Mediates microtubule polyglutamylation in primary cilia axoneme, which is important for ciliary structural formation and motility. Mediates microtubule polyglutamylation in motile cilia, necessary for the regulation of ciliary coordinated beating. Polyglutamylates non-tubulin protein nucleotidyltransferase CGAS, leading to CGAS DNA-binding inhibition, thereby preventing antiviral defense response. ATP + L-glutamate + L-glutamyl-[protein] = ADP + gamma-L-glutamyl-L-glutamyl-[protein] + H(+) + phosphate (L-glutamyl)(n)-gamma-L-glutamyl-L-glutamyl-[protein] + ATP + L-glutamate = (L-glutamyl)(n+1)-gamma-L-glutamyl-L-glutamyl-[protein] + ADP + H(+) + phosphate Found in a complex with CEP41. CEP41 is required for its transport between the basal body and the cilium axoneme. The flexible c-MTBD (cationic microtubule binding domain) region mediates binding to microtubules. It is positively charged and becomes ordered when bound to microtubules: it interacts with a negatively charged patch on tubulin. The presence of positive charges in the c-MTBD region is essential for proper binding. Gln-181 is the main determinant for regioselectivity, which segregates between initiases and elongases in all tubulin--tyrosine ligase family. A glutamine residue at this position is found in elongases TTLL6, TTLL9, TTLL11, TTLL13, TTLL10 and favors glutamate-chain elongation, whereas an arginine residue is found in initiases TTLL2, TTLL4, TTLL5, TTLL3, TTLL8 and favors initiation. Belongs to the tubulin--tyrosine ligase family. Truncated N-terminus.