This domain is found in the C-terminal region of the TRIM subgroup C-1 proteins such as E3 ubiquitin-protein ligase Midline-1 protein which is required for the proper development during embryogenesis. Mutations of MID1 are associated with X-linked Opitz G syndrome, characterized by midline anomalies. This domain is also found in MURF1-3 proteins that do not contain the FNIII and B30.2 domains. MUF1-3 proteins are also associated with microtubules. Deletion of the COS domain does not affect MID1 dimerization but disrupts the localization to the microtubules [1].

1: Solution structure of the microtubule-targeting COS domain of MID1. Wright KM, Du H, Dagnachew M, Massiah MA; FEBS J. 2016;283:3089-3102. PMID:27367845