Isolation and molecular characterization of the porcine stearoyl-CoA desaturase gene.

Stearoyl-CoA desaturase (SCD) is a rate-limiting enzyme in the biosynthesis of unsaturated fatty acids. So far only a partial porcine SCD sequence is available. Here we described the isolation and molecular characterization of the full-length cDNA and the determination of the genomic DNA sequence of the porcine SCD gene. The 5134-bp cDNA contains a 1080-bp open reading frame (ORF) encoding a protein of 359 amino acids with a calculated molecular mass of 41.3 kDa and a theoretical isoelectric point of 9.4. The porcine SCD protein shares high identity (>80%) with the other mammalian SCD. To further elucidate the genomic structure of the porcine SCD gene, we sequenced 20,985 bp of genomic DNA sequence encompassing the complete pig SCD gene. Similar to the other mammalian orthologs, particularly in term of exon size and exon/intron boundaries, the porcine SCD gene spans a transcription unit of 16,186 bp, consisting of six exons with sizes ranging from 131 to 4048 bp, and five introns varying in size from 518 to 4784 bp. The gene reveals a 176-bp-long 5' UTR and possesses an unusually long 3'UTR of 3848 bp in the last exon. Comparison of different mammalian SCD promoters identified some regulatory domains required for the transcription regulation in the 5' flanking sequence of the porcine SCD gene, such as the conserved polyunsaturated fatty acid response region (PUFA-RE). A total of 21 gene polymorphisms were revealed in the 21-kb DNA sequence, including 19 single nucleotide polymorphisms (SNPs), a 24-bp-long fragment length polymorphism in the fourth intron and a triplet nucleotide insertion in the fifth intron. Reverse transcription (RT)-PCR result indicates that the SCD gene is expressed ubiquitously in pigs.