RING-CH finger, H2 subclass (C4HC3-type), found in transcriptional repressor NF-X1 and similar proteins
NF-X1, also known as nuclear transcription factor, X box-binding protein 1, is a novel cysteine-rich sequence-specific DNA-binding protein that interacts with the conserved X-box motif of the human major histocompatibility complex (MHC) class II genes via a repeated Cys-His domain. It functions as a cytokine-inducible transcriptional repressor that plays an important role in regulating the duration of an inflammatory response by limiting the period in which class II MHC molecules are induced by interferon gamma (IFN- gamma). NFX1 contains an N-terminal PAM2 motif, a C4HC3-type RING-CH finger, a Cys-rich region that harbors several NFX1-type zinc fingers, and a C-terminal R3H domain.
Comment:A RING finger typically binds two zinc atoms, with its Cys and/or His side chains in a unique "cross-brace" arrangement.
Comment:The RING fingers found in NFX1 and its homologs have an unusual arrangement of zinc-coordinating residues: The conserved helix complete with tryptophan at the C-terminal end is present but the cysteines and histidines are arranged in the sequence as C4HC3-type, rather than the typical C3H2C3-type in RING-H2 finger.
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