Genomic organization of the porcine dopachrome tautomerase (DCT) gene

Dopachrome tautomerase (DCT) is an enzyme that isomerizes the melanogenic intermediate 3,4-dihydroxyphenylalanine-chrome (DOPAchrome) to 5,6-dihydroxyindole-2-carboxylic acid (DHICA) in the biosynthesis of melanin. In this study, we extracted the porcine bacterial artificial chromosome (BAC) clone containing the entire DCT gene and then sequenced it completely to determine its genomic structure. The BAC clone sequence was 127 098 bp in length. Compared to the DCT gene coding sequence determined in our previous study, the DCT gene structure determined in the current study comprised eight exons spanning 50.3 kbp of the genomic DNA, and the sequences from exon 7-9 of the glypican 6 (GCP6) gene were also detected in this clone. The gene order and the transcriptional orientation of the porcine genomic region in this BAC clone were identical to those of the corresponding human genomic region. In addition, we cloned three transcripts by using the 5'-rapid amplification of cDNA ends (RACE) method in combination with alternative promoter usage and alternative splicing. Two 3'-RACE products differed in the poly(A) addition site. Three 5'-RACE clones differed in exon 1 that codes for a signal peptide that is important for the cytoplasmic trafficking of premature DCT; however, the relationship between the alternative transcripts and pig coat color is unclear.