Molecular cloning and analyzing of fatty acid desaturase and elongase genes in grass carp(Ctenopharyngodon idellus)

Full-length cDNAs of fatty acid desaturase(FAD) and fatty acid elongase(ELO),which were involved in the biosynthesis of highly unsaturated fatty acids(HUFA),were isolated from grass carp(Ctenopharyngodon idellus),based on RT-PCR and RACE methods.The FAD cDNA was 1 994 bp,including an ORF of 1 332 bp specifying a protein of 444 amino acids.The protein sequence contained all the characteristics of microsomal fatty acid desaturases,including 3 histidine boxes,2 transmembrane regions,and a cytochrome b5 domain.The deduced amino acid sequence shared 63.5%-70.5% identity with other fishes,and the phylogenetic tree showed that it clustered closely with herbivore freshwater fish.The 1 131 bp cDNA of ELO included an 876 bp ORF encoding a 445 amino acid peptide that contained one single histidine box redox centre motif,one canonical ER retention signal and several transmembrane regions,in line with other fatty acid elongases.The protein sequence had 70.6%-89.3% identity with other fishes,and the phylogenetic tree showed that it clustered closely with herbivorous and omnivorous freshwater fish.These results will help study the relationship between their structure and function,and elucidate the HUFA biosynthesis pathway in grass carp.