β-ketoacyl-ACP synthase (EC 126.96.36.199) (KAS)  is the enzyme that
catalyzes the condensation of malonyl-ACP with the growing fatty acid chain.
It is found as a component of the following enzymatic systems:
Fatty acid synthase (FAS), which catalyzes the formation of long-chain
fatty acids from acetyl-CoA, malonyl-CoA and NADPH. Bacterial and plant
chloroplast FAS are composed of eight separate subunits which correspond to
different enzymatic activities; β-ketoacyl synthase is one of these
polypeptides. Fungal FAS consists of two multifunctional proteins, FAS1 and
FAS2; the β-ketoacyl synthase domain is located in the C-terminal
section of FAS2. Vertebrate FAS consists of a single multifunctional chain;
the β-ketoacyl synthase domain is located in the N-terminal section .
The multifunctional 6-methysalicylic acid synthase (MSAS) from Penicillium
patulum . This is a multifunctional enzyme involved in the biosynthesis
of a polyketide antibiotic and which has a KAS domain in its N-terminal
Polyketide antibiotic synthase enzyme systems. Polyketides are secondary
metabolites produced by microorganisms and plants from simple fatty acids.
KAS is one of the components involved in the biosynthesis of the
Streptomyces polyketide antibiotics granatacin , tetracenomycin C 
Emericella nidulans multifunctional protein Wa. Wa is involved in the
biosynthesis of conidial green pigment. Wa is protein of 216 Kd that
contains a KAS domain.
Rhizobium nodulation protein nodE, which probably acts as a β-ketoacyl
synthase in the synthesis of the nodulation Nod factor fatty acyl chain.
Yeast mitochondrial protein CEM1.
The condensation reaction is a two step process: the acyl component of an
activated acyl primer is transferred to a cysteine residue of the enzyme and
is then condensed with an activated malonyl donor with the concomitant release
of carbon dioxide. The sequence around the active site cysteine is well
conserved and can be used as a signature pattern.
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