Also known as: His₆-hHR6A (human Homolog of RAD6A)

The human HR6A and HR6B proteins share about 95% amino acid sequence identity with each other and about 70% with yeast counterparts, but notably lack the acidic C-terminal domain found in S. cerevisiae proteins. The RAD6 pathway is essential to post-replication repair of DNA and damage-induced mutagenesis in eukaryotic cells. hHR6 protein expression is cell cycle regulated and function with RAD5 and RAD18 RING-finger proteins. The human proteins function similar to the yeast homologs, and may have additional roles in chromatin remodeling and spermatogenesis Residue Ser¹²⁰ is an important regulatory site in hHR6A, being phosphorylated in vitro by CDK1/2 on which increases ubiquitin conjugating activity. A nonsense mutation in hHR6A has been linked to a novel X-linked mental retardation syndrome (XMLR). This protein has an N-terminal His₆ tag, Accession NP_003327.