Polyglutamylase which preferentially modifies tubulin (PubMed:29129530, PubMed:27635036). Involved in the side-chain initiation step of the polyglutamylation reaction (PubMed:29129530, PubMed:27635036). By controlling tubulin glutamylation, regulates ciliary specialization and motor-based transport. Promotes the formation of A and B tubule singlets by splaying microtubule doublets in cilia (PubMed:29129530). Together with ttll-4 and 5, required for male mating (PubMed:27635036). Specifically promotes tubulin glutamylation in a subset of ciliated neurons including amphid, phasmid, CEP and RnA neurons. Specifically promotes tubulin glutamylation in male ciliated CEM, HOB and RnB neurons that release bioactive extracellular vesicles (PubMed:29129530). Regulates the localization of TRP channel pdk-2 in male CEM, HOB and RnB neurons (PubMed:29129530). Regulates the environmental release of bioactive extracellular vesicles in cilia (PubMed:29129530). ATP + L-glutamate + L-glutamyl-[protein] = ADP + gamma-L-glutamyl-L-glutamyl-[protein] + H(+) + phosphate Expressed in amphid sensory neurons (PubMed:20519502, PubMed:29129530). Weakly expressed in body wall muscles (PubMed:20519502). Isoform a: Specifically expressed in ciliated sensory neurons in the head, including the IL1s, OLQ, head CEP, and amphid neurons. In the male tail, expressed in HOA, RnA, and phasmid neurons (PubMed:29129530). Isoform b: Specifically expressed in male and hermaphrodite IL2 ciliated sensory neurons, and in male-specific CEM, HOB and RnB ciliated sensory neurons (PubMed:29129530). Expressed in embryos and adults. Belongs to the tubulin--tyrosine ligase family.