ERH(enhancer of rudimentary homolog) belongs to the E(R) family. It is expressed in all tissues examined. The monomeric structure of ERH comprises a single domain consisting of three α-helices and four β-strands, which is a novel fold. In the crystal structure, ERH assumes a dimeric structure, through interactions between the β-sheet regions. The formation of an ERH dimer is consistent with the results of analytical ultracentrifugation. ERH may have a role in the cell cycle. The Drosophila protein ERH is a small protein of 14 amino acids. It has been found to be an enhancer of the rudimentary gene, involved in pyrimidine biosynthesis. From an evolutionary point of view, ERH is highly conserved and has been found to exist in probably all multicellular eukaryotic organisms. ERH interacts with POLDIP3.