PRIMARY STRUCTURE OF A CERULENIN-BINDING BETA-KETOACYL-[ACYL CARRIER PROTEIN] SYNTHASE FROM BARLEY CHLOROPLASTS

The radioactively labeled beta-ketoacyl thioester synthase inhibitor [H-3]cerulenin was used to tag three dimeric barley chloroplast proteins (alpha-alpha, alpha-beta, and beta-beta) from the stromal fraction. Oligonucleotides corresponding to amino acid sequences obtained from the purified proteins were used to generate with the polymerase chain reaction a probe for cDNAs encoding the beta-subunit. cDNA sequencing revealed an open reading frame for 462 residues comprising the mature protein and a 35-amino acid transit peptide. The deduced amino acid sequence of the mature protein is homologous to the beta-ketoacyl[acyl carrier protein] (ACP) synthase I [3-oxoacyl-ACP synthase; acyl-ACP:malonyl-ACP C-acyltransferase (decarboxylating), EC 2.3.1.41] of Escherichia coli. Under analogous experimental conditions [H-3]cerulenin tagged a single dimeric protein from spinach chloroplasts.