The Rel homology domain (RHD) is a protein domain found in a family of eukaryotic transcription factors, which includes NF-κB, NFAT, among others. Some of these transcription factors appear to form multi-protein DNA-bound complexes.Phosphorylation of the RHD appears to play a role in the regulation of some of these transcription factors, acting to modulate the expression of their target genes. The RHD is composed of two immunoglobulin-like beta barrel subdomains that grip the DNA in the major groove. The N-terminal specificity domain resembles the core domain of the p53 transcription factor, and contains a recognition loop that interacts with DNA bases. The C-terminal dimerization domain contains the site for interaction with I-kappaB.