STRUCTURAL ORGANIZATION OF THE HUMAN MICROSOMAL GLUTATHIONE-S-TRANSFERASE GENE (GST12)

The primary structure of the human microsomal glutathione S-transferas e gene (GST12) was determined by genomic cloning. The gene structure o f GST12 spans 12.8 kb and consists of four exons and three introns. Th e coding sequence resides on exons 2, 3, and 4. Sequencing of the exon s revealed two nucleotide differences compared to a previous report of the cDNA sequence. The substitutions, however, were silent, as they d id not alter amino acid composition or restriction enzyme sites. All i ntrons commenced with nucleotides GTAA at the 5' boundary and ended wi th nucleotides AG at the 3' boundary, in agreement with the proposed c onsensus sequence for intron spliced donor and acceptance sites. The p resence of an in-phase stop codon and an upstream false start codon in the 5'-untranslated region was confirmed. Although it was previously predicted that there existed another start codon in-phase and within 5 0 bp of this stop codon, coding for a second mini-cistron, we could no t identify another start codon for greater than 200 bp prior to the st op codon. Thus, initiation is suppressed at the first or false start c odon due to either the closeness of the stop codon or the suboptimal c ontext of the codon. (C) 1996 Academic Press, Inc.