This family includes small CPxCG-related zinc finger archaeal proteins, which are typically between 200 and 221 amino acids in length. They are likely to bind DNA and to be potential transcriptional regulators. These zinc fingers are characterised by the specific CPxCG pattern (variants CPxCx and CxxCG) and a second Cys/His pattern potentially more general, being 7-40 residues apart, forming a zinc finger motif. This family contains the specific CxxCG motif and the Cys motif (CPxCx) at the N-terminal. A member of this family, the Nif-regulating protein A Swiss:Q8PW88, contains the patterns CxxCG and HxxxH (the latter unique to this protein, located 24 residues away from the CxxCG pattern) to form the zinc finger motif. It is a DNA-binding protein that enhances the transcription of the nitrogen fixation (nif) operon under nitrogen-limited conditions [1].

1: The transcriptional activator NrpA is crucial for inducing nitrogen fixation in Methanosarcina mazei Go1 under nitrogen-limited conditions. Weidenbach K, Ehlers C, Schmitz RA; FEBS J. 2014;281:3507-3522. PMID:24930989