RING finger family found sporadically in bacteria and archaea, and associated with other components of the ubiquitin-based signaling and degradation system, including ubiquitin and the E1 and E2 proteins. The bacterial versions contain transmembrane helices [1].

1: Functional diversification of the RING finger and other binuclear treble clef domains in prokaryotes and the early evolution of the ubiquitin system. Burroughs AM, Iyer LM, Aravind L; Mol Biosyst. 2011;7:2261-2277. PMID:21547297