Production of polyunsaturated fatty acids by polyketide synthases in both prokaryotes and eukaryotes

Polyunsaturated fatty acids (PUFAs) are essential membrane components in hi gher eukaryotes and are the precursors of many lipid-derived signaling mole cules. Here, pathways for PUFA synthesis are described that do not require desaturation and elongation of saturated fatty acids. These pathways are ca talyzed by polyketide synthases (PKSs) that are distinct from previously re cognized PKSs in both structure and mechanism. Generation of cis double bon ds probably involves position-specific isomerases; such enzymes might be us eful in the production of new families of antibiotics. it is Likely that PU FA synthesis in cold marine ecosystems is accomplished in part by these PKS enzymes.