WDR4 (WD repeat-containing protein 4) was identified in a search for candidate genes involved in the development of Down syndrome phenotypes. It is required for the 7-methylguanosine (m7G)-methyltransferase activity for tRNA. WDR bears two WD repeats. The WD repeat is defined by four or more repeating units of a conserved core of approximately 40 amino acids ending with tryptophan-aspartic acid (WD). WD repeats may serve as sites of protein-protein interaction for adaptor proteins and facilitate multiprotein complex formation.