ISOLATION AND CHARACTERIZATION OF A MAIZE CDNA THAT COMPLEMENTS A 1-ACYL SN-GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE MUTANT OF ESCHERICHIA-COLIAND ENCODES A PROTEIN WHICH HAS SIMILARITIES TO OTHER ACYLTRANSFERASES

We selected cDNA plasmid clones that corrected the temperature-sensiti ve phenotype of Escherichia coli strain JC201, which is deficient in 1 -acyl-sn-glycerol-3-phosphate acyltransferase activity. A plasmid-base d maize endosperm cDNA library was used for complementation and a plas mid that enabled the cells to grow at 44 degrees C on ampicillin was i solated. Addition of this plasmid (pMAT1) to JC201 restored 1-acyl-sn- glycerol-3-phosphate acyltransferase activity to the cells. Total phos pholipid labelling showed that the substrate for the enzyme, lysophosp hatidic acid, accumulated in JC201 and was further metabolised to phos phatidylethanolamine in complemented cells. Membranes isolated from su ch cells were able to convert lysophosphatidic acid to phosphatidic ac id in acyltransferase assays. The cDNA insert of pMAT1 contains one lo ng open reading frame of 374 amino acids which encodes a protein of re lative molecular weight 42 543. The sequence of this protein is most s imilar to SLC1, which is thought to be able to acylate glycerol at the sn-2 position during synthesis of inositol-containing lipids. Homolog ies between the SLC I protein, the 1-acyl-sn-glycerol-3-phosphate acyl transferase of E. coli (PlsC) and the maize ORF were found with blocks of conserved amino acids, whose spacing was conserved between the thr ee proteins, identifiable.