MOLECULAR-CLONING OF THE HUMAN LEUKOTRIENE C-4 SYNTHASE GENE AND ASSIGNMENT TO CHROMOSOME 5Q35

Background: Cysteinyl leukotrienes (LT) are mediators involved in infl ammatory and allergic disorders. LTC(4) synthase catalyzes the first c ommitted step in the syn thesis of these inflammatory mediators, and i ts cellular distribution appears to be unique. Materials and Methods: A human genomic library was screened by polymerase chain reaction (PCR ) with primers that were designed based on the reported cDNA sequence for the LTC(4) synthase gene. The gene was identified in one clone by Southern blotting of restriction enzyme digests, subcloning of fragmen ts containing regions of interest, and DNA sequencing of these subclon es. The transcription initiation site was determined by primer extensi on analysis. Chromosome location was determined by fluorescent in situ hybridization and screening of somatic cell hybrids by PCR. Results: The LTC(4) synthase gene is similar to 2.5 kb in length, consisting of five exons (136, 100, 71, 82, and 257 bp, respectively) and four intr ons (1,447, 102, 84, and 230 bp, respectively). Transcription initiati on occurs at a single site 78 bp upstream of the coding region. The 5' -flanking region contains neither a TATA nor a CAAT box. The first 1 k b of the 5'-flanking region, however, contains putative DNA binding mo tifs for SP-l, AP-1, AP-2, els factors, and CREB/ATF. A STAT binding m otif is present in the first intron. The LTC(4) synthase gene is locat ed in the distal region of the long arm of chromo-some 5 in 5q35. Conc lusions: The LTC, synthase gene does not contain elements of a typical regulated gene and may therefore contain novel regulatory elements. T his gene is also located in a region on chromosome 5 that appears to p lay a role in allergic and inflammatory disorders, such as asthma.