C-terminal domains (CTDs) of ABC-3C systems, contain distinct patterns of charged and polar residues and are not yet unifiable with known domains. These domains are found at the C-terminus of the effector component of the systems, which are upstream of the Middle Component and ABC ATPase components on the genome. Due to the typically large size of these CTDs relative to the actual effector and MC domains, the CTDs are predicted to serve as the platform on which the remaining two components assemble. Therewith, conformational changes transmitted by the ABC ATPase-mediated detection of invasive elements like DNA viruses would result in an unfurling and activation of the CTD-associated effector [1].

1: Comprehensive classification of ABC ATPases and their functional radiation in nucleoprotein dynamics and biological conflict systems. Krishnan A, Burroughs AM, Iyer LM, Aravind L; Nucleic Acids Res. 2020;48:10045-10075. PMID:32894288