CHARACTERIZATION OF THE FAD12 MUTANT OF SYNECHOCYSTIS THAT IS DEFECTIVE IN DELTA-12 ACYL-LIPID DESATURASE ACTIVITY

The Fad12 mutant of Synechocystis sp. PCC 6803 has a defect in the des A gene for Delta 12 acyl-lipid desaturase. We identified a change in t he nucleotide sequence of the structural gene for the desaturase, in w hich a leucine codon has been converted to a stop codon, Western blot analysis revealed that the Delta 12 acyl-lipid desaturase was localize d in both plasma membranes and thylakoid membranes of wild-type cells but was absent from both types of membrane in Fad12 cells. These findi ngs suggest that the desaturation of fatty acids takes place in both t ypes of membrane in Synechocystis sp. PCC 6803. The mutation in the De lta 12 desaturase did not affect the lipid composition of thylakoid an d plasma membranes, but it changed the fatty acid composition of lipid s in similar ways in both types of membrane.