Isolation of a ?6-desaturase gene from the cyanobacterium Synechocystis sp. strain PCC 6803 by gain-of-function expression in Anabaena sp.strain PCC 7120

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Abstract
The enzyme Δ6-desaturase is responsible for the conversion of linoleic acid (18:2) to γ-linolenic acid (18:3γ). A cyanobacterial gene encoding Δ6-desaturase was cloned by expression of a Synechocystis genomic cosmid library in Anabaena, a cyanobacterium lacking Δ6-desaturase. Expression of the Synechocystis Δ6-desaturase gene in Anabaena resulted in the accumulation of γ-linolenic acid (GLA) and octadecatetraenoic acid (18:4). The predicted 359 amino acid sequence of the Synechocystis Δ6-desaturase shares limited, but significant, sequence similarity with two other reported desaturases. Analysis of three overlapping cosmids revealed a Δ12-desaturase gene linked to the Δ6-desaturase gene. Expression of Synechocystis Δ6-and Δ12-desaturase in Synechococcus, a cyanobacterium deficient in both desaturases, resulted in the production of linoleic acid and γ-linolenic acid.