Phosphatidylinositol, phosphatidylglycerol and phosphatidylserine are syn-thesised from PA via CDP-diacylglycerol (CDP-DAG). The enzyme CDP-DAG synthase (CDS) uses PA and CTP as substrates and releases phosphatidyl-inositol phosphate in addition to the CDP-DAG (Fig. 2, step 1). cDNAs encoding CDP-DAG synthases were cloned from potato and Arabidopsis using knowledge of sequence homology, and CDS activity was proved by expression of cDNA in E. coli combined with purification of the protein (Kopka et al. 1997). Arabidopsis is predicted to contain two ER-bound CDS genes, each predicted to contain eight membrane spanning domains, but little analysis of their function in plants has been reported. The head group of the phospho-lipid is then attached to the lipid by displacement of CMP from CDP-DAG (Fig. 2).
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