Cloning and Functional Identification of Delta5 Fatty Acid Desaturase Gene and Its 5′-Upstream Region from Marine Fungus Thraustochytrium sp. FJN-10

A gene encoding delta5 fatty acid desaturase (fad5) was cloned from marine fungus Thraustochytrium sp. FJN-10, a species capable of producing docosahexaenoic acid. The open reading frame of fad5 was 1,320 bp and encoded a protein comprising 439 amino acids. Expression of the fad5 in Saccharomyces cerevisiae INVSC1 revealed that FAD5 is able to introduce a double bond at position 5 of the dihomo-γ-linolenic acid (20:3 Δ8,11,14), resulting in arachidonic acid (20:4 Δ5,8,11,14) with a conversion rate of 56.40% which is the highest among engineering yeasts reported so far. The 5′-upstream region of fad5 was cloned by LA-PCR and analyzed. Phylogenetic analysis of this sequence with the 5′-upstream region of other delta5 desaturases showed that the 5′-upstream region of fad5 from Thraustochytrium share the smallest evolution distance with human and rhesus. Computational analysis of the nucleotide sequence of the 5′-upstream region of fad5 has revealed several basic transcriptional elements including five TATA boxes, three CCAAT boxes, 12 GC boxes, and several putative target-binding sites for transcription factors such as HSF, CAP, and ADR1. Preliminary functional analysis of this promoter in S. cerevisiae shows that the 5′-upstream region of fad5 could drive the expression of green fluorescent protein.