STRUCTURE OF THE HUMAN GENE ENCODING THE PROTEIN REPAIR L-ISOASPARTYL(D-ASPARTYL) O-METHYLTRANSFERASE

The protein L-isoaspartyl/D-aspartyl O-methyltransferase (EC 2.1.1.77) catalyzes the first step in the repair of proteins damaged in the agi ng process by isomerization or racemization reactions at aspartyl and asparaginyl residues. A single gene has been localized to human chromo some 6 and multiple transcripts arising through alternative splicing h ave been identified. Restriction enzyme mapping, subcloning, and DNA s equence analysis of three overlapping clones from a human genomic libr ary in bacteriophage P1 indicate that the gene spans approximately 60 kb and is composed of 8 exons interrupted by 7 introns. Analysis of in tron/exon splice junctions reveals that all of the donor and acceptor splice sites are in agreement with the mammalian consensus splicing se quence. Determination of transcription initiation sites by primer exte nsion analysis of poly(A)(+) mRNA from human brain identifies multiple start sites, with a major site 159 nucleotides upstream from the ATG start codon, Sequence analysis of the 5'-untranslated region demonstra tes several potential cis-acting DNA elements including SP1, ETF, AP1, AP2, ARE, XRE, CREB, MED-1, and half-palindromic ERE motifs. The prom oter of this methyltransferase gene lacks an identifiable TATA box but is characterized by a CpG island which begins approximately 723 nucle otides upstream of the major transcriptional start site and extends th rough exon 1 and into the first intron. These features are characteris tic of housekeeping genes and are consistent with the wide tissue dist ribution observed for this methyltransferase activity. (C) 1996 Academ ic Press, Inc.