STRUCTURE, PROMOTER ANALYSIS AND CHROMOSOMAL ASSIGNMENT OF THE HUMAN APEX GENE

APEX nuclease is a mammalian DNA repair enzyme having apurinic/apyrimi dinic endonuclease, 3'-5'-exonuclease, DNA 3' repair diesterase and DN A 3'-phosphatase activities. This report describes the organization of the gene (APEX gene) for human APEX nuclease. Human APEX gene was clo ned using human APEX cDNA and a human leukocyte genomic library in bac teriophage vector EMBL-3, We proved that human APEX gene consists of 5 exons spanning 2.64 kilobases and suggested that the gene exists as a single copy in the haploid genome. The boundaries between exon and in tron follow the GT/AG rule. The major transcription initiation site wa s assigned by primer extension analysis to C at 515 nucleotides upstre am from the ATG initiation codon. The translation initiation and termi nation sites locate in the exon II and V, respectively. The 5' flankin g region (0.89 kilobase) sequenced lacks typical TATA and CAAT boxes, but contains TATA- and CAAT-like sequences and putative cis-acting reg ulatory elements such as binding sites for Spl, AP2 and ATF. A part of the 5' flanking region belongs to a CpG island, which extends to the intron II. The CPG island is thought to be a transcription regulatory region of APEX gene, a housekeeping gene. The promoter activity of the 5' upstream region was analyzed by introducing the region in HeLa cel ls in an expression construct containing luciferase gene as a reporter gene,and the region from position 130 bp upstream to position 205 bp downstream of the major transcription initiation site was shown to be enough for high promoter activity. Northern hybridization experiments suggested that the gene is expressed ubiquitously in human cells. The locus of APEX gene was mapped to human chromosome 14q11.2-q12 using th e in situ hybridization technique.