Negatively regulates post-translational modifications of tubulin, including detyrosination of the C-terminus and polyglutamylation of glutamate residues (PubMed:20162578, PubMed:23251473). Also, indirectly promotes histone H4 trimethylation at 'Lys-20' (H4K20me3) (PubMed:23251473). Probably by controlling tubulin and/or histone H4 post-translational modifications, plays a role in mitosis and in maintaining chromosome number stability (PubMed:20162578, PubMed:23251473). During RNA virus-mediated infection, acts as a negative regulator of the DDX58/RIG-I pathway by preventing MAVS binding to TBK1 and IKBKE (PubMed:28011935). Interacts with MAVS; the interaction prevents MAVS binding to TBK1 and IKBKE (PubMed:28011935). Interacts (via N-terminus) with TBK1 (via protein kinase domain) (PubMed:28011935). Interacts (via TTL domain) with IKBKE (via protein kinase domain) (PubMed:28011935). Interacts with tubulin alpha (PubMed:23251473). Interacts with histone H3 and histone H4 (when trimethylated at 'Lys-20' (H4K20me3)) (PubMed:23251473). Interacts with CBX3 (PubMed:23251473). Predominantly localizes in the cytoplasm (PubMed:28011935). Partially colocalizes with vimentin in prostate cancer cells (PubMed:20162578). Expressed in the basal layer of prostate and endothelial cells. Increased expression in prostatic intraepithelial neoplasia and metastatic lesions. 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 (PubMed:23251473). Lacks tyrosine ligase activity in vitro (PubMed:23251473). Lacks glutamylation activity in vitro (By similarity). Although TTLL12 contains a potential SET-like domain in the N-terminus, it does not have lysine methyltransferase activity towards histone in vitro (PubMed:23251473).