Imprinting of the Angelman syndrome gene, UBE3A , is restricted to brain

E6-AP ubiquitin protein ligase 3A (UBE3A) transfers ubiquitin to protein substrates in the ubiquitin-proteosome proteolytic pathway. super(1) Loss of enzyme function due to truncating mutations in the coding region of the gene super(2,3) was found in patients with Angelman syndrome (AS). AS is characterized by severe mental retardation, which is frequently associated with deletion of maternal chromosome 15q11-13, suggesting that the AS gene is paternally imprinted super(4,5). Although UBE3A was identified as the AS gene super(2,3), its expression is biallelic in fibroblasts and lymphoblasts super(6). We have identified a novel polymorphic site and have quantitated UBE3A allelic expression in various human fetal tissues. In heart and kidney, transcripts of UBE3A from two putative promoter regions were derived from both parental alleles, while transcripts from both promoters were derived predominantly from a single parental allele in the central nervous system. To identify promoter exons, we amplified the 5' end of UBE3A mRNAs by 5'-RACE, and identified multiple isoforms.