They are found in TRIM (tripartite motif) proteins that consist of an N-terminal RING finger (originally called an A-box), followed by 1-2 B-box domains and a coiled-coil domain (also called RBCC for Ring, B-box, Coiled-Coil).

[1] The microtubule-associated E3 ligase MID1 (EC) contains a type 1 B-box zinc finger domain.

[2][3] Prokaryotic homologs of the domain are present in several bacterial lineages and methanogenic archaea, and often show fusions to peptidase domains such as the rhomboid-like serine peptidase, and Zn-dependent metallopeptidase.

Other versions typically contain transmembrane helices and might also show fusions to domains such as DNAJ, FHA, SH3, WD40 and tetratricopeptide repeats.

Together these associations suggest a role for the prokaryotic homologs of the B-box zinc finger domain in proteolytic processing, folding or stability of membrane-associated proteins.