Negatively regulates post-translational modifications of tubulin, including detyrosination of the C-terminus and polyglutamylation of glutamate residues. Also, indirectly promotes histone H4 trimethylation at 'Lys-20' (H4K20me3). Probably by controlling tubulin and/or histone H4 post-translational modifications, plays a role in mitosis and in maintaining chromosome number stability. During RNA virus-mediated infection, acts as a negative regulator of the DDX58/RIG-I pathway by preventing MAVS binding to TBK1 and IKBKE. Interacts with MAVS; the interaction prevents MAVS binding to TBK1 and IKBKE. Interacts (via N-terminus) with TBK1 (via protein kinase domain). Interacts (via TTL domain) with IKBKE (via protein kinase domain). Interacts with tubulin alpha. Interacts with histone H3 and histone H4 (when trimethylated at 'Lys-20' (H4K20me3)). Interacts with CBX3. Predominantly localizes in the cytoplasm. Widely expressed with highest levels in brain, kidney, liver, lung, muscle and testis. Belongs to the tubulin--tyrosine ligase family. Although it belongs to the tubulin--tyrosine ligase family, the TTL domain lacks some of the ATP binding sites predicted to be essential for TTL activity (By similarity). Lacks tyrosine ligase activity in vitro (By similarity). Lacks glutamylation activity in vitro (PubMed:17499049). Although TTLL12 contains a potential SET-like domain in the N-terminus, it does not have lysine methyltransferase activity towards histone in vitro (By similarity).