Molecular Cloning of Full-Length Cdna Encoding Delta-9 Desaturase through Pcr Strategies and Its Genomic Organization and Expression in Grass Carp.

Desaturases are enzymes that catalyze double bond formation in fatty acids, which is a critical step in the synthesis of unsaturated fatty acids in organisms. Desaturase cDNA has been cloned from various species. Here we report the cloning of a full-length cDNA of D9 - desaturase from grass carp ( Ctenopharyngodon idella), using a combination of PCR techniques: reverse transcription±polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The resolved cDNA encompasses 2420 bp, containing an open reading frame correspon-ding to 324 amino acids. The deduced amino acid sequence shares high homology with those of mam- malian desaturases. Northern blot and RT-PCR ana-lyses demonstrated a high abundance of the transcript in liver tissue but low abundance in brain tissue. Furthermore, the structure of the gene has been re-solved by screening its cognate genomic DNA library. The analysis shows that this gene is composed of six exons and five introns, encompassing a region of 8 .5 kb. In particular, the last exon contains a length of the 30 untranslated region as long as 1382 bp. Although the primary sequence and the genomic organization are phylogenetically conserved between fish and mammals, the regulation of the gene expression appears to be divergent among species.