title: Isolation and characterization of the beta-ketoacyl-acyl carrier protein synthase III gene (fabH) from Escherichia coli K-12.
abstract: beta-Ketoacyl-acyl carrier protein (ACP) synthase III catalyzes the condensation of acetyl-CoA with malonyl-ACP in dissociated (Type II) fatty acid synthase systems. A synthase III mutant was used to localize the structural gene to the 24.5-min region of the Escherichia coli chromosome, and the defective synthase III allele was designated fabH1. The fabH gene was identified on a 1.3-kilobase NruI-HindIII chromosomal DNA fragment (plasmid pWO114) that complemented the enzymatic defect in fabH1 strains. The NruI-HindIII fragment was sequenced and contained a single open reading frame predicted to encode a 33,517-dalton protein with an isoelectric point of 4.85. The fabH sequence contained an Ala-Cys-Ala tripeptide characteristic of condensing enzyme active sites. A T7 expression system showed that the NruI-HindIII fragment directed the synthesis of a single 34,800-dalton protein. This protein was purified and the order of the amino-terminal 30 residues of the protein corresponded exactly to the amino acid structure predicted from the DNA sequence. The purified protein possessed both acetoacetyl-ACP synthase and acetyl-CoA:ACP transacylase activities, and cells harboring plasmid pWO114 overproduced the two activities, supporting the conclusion that a single protein carries out both reactions. Overproduction of synthase III resulted in a significant increase in shorter-chain fatty acids in the membrane phospholipids. These catalytic properties are consistent with the proposed role of synthase III in the initiation of fatty acid synthesis.
authors.affiliation: Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
authors.forename: J T
authors.initials: JT
authors.lastname: Tsay
authors.forename: W
authors.initials: W
authors.lastname: Oh
authors.forename: T J
authors.initials: TJ
authors.lastname: Larson
authors.forename: S
authors.initials: S
authors.lastname: Jackowski
authors.forename: C O
authors.initials: CO
authors.lastname: Rock
mesh_terms: D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D005227:Fatty Acids / Q000032:analysis / Q000096:biosynthesis; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D010957:Plasmids; D015183:Restriction Mapping; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
chemical_list: D005227:Fatty Acids; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase