text: The biosynthesis of lovastatin occurs via an iterative type I polyketide synthase (PKS) pathway. The six genes that encode enzymes that are essential for the biosynthesis of lovastatin are lovB, lovC, lovA, lovD, lovG, and lovF . The synthesis of dihydromonacolin L requires a total of 9-malonyl Coa . It proceeds in the PKS pathway until it reaches (E) a hexaketide, where it undergoes a Diels-Alder cycloaddition to form the fused rings. After cyclization it continues through the PKS pathway until it reaches (I) a nonaketide, which then undergoes release from LovB through the thioesterase encoded by LovG. Dihydromonacolin L, (J), then undergoes oxidation and dehydration via a cytochrome P450 oxygenase encoded by LovA to obtain monacolin J, (L).
  The MT domain from lovB is active in the conversion of (B) to (C) when it transfers a methyl group from S-adenosyl-L-methionine (SAM) to the tetraketide (C) . Owing to the fact that LovB contains an inactive ER domain, LovC is required at specific steps to obtain fully reduced products. The domain organization of LovB, LovC, LovG and LovF is shown in Figure 2. The inactive ER domain of lovB is shown with an oval and where LovC acts in trans to LovB is shown with a red box.
  In a parallel pathway, the diketide side chain of lovastatin is synthesized by another highly reducing type I polyketide synthase enzyme encoded by LovF . Lastly, the side chain, 2-methylbutyrate (M) is covalently attached to C-8 hydroxy group of monacolin J (L) by a transesterase encoded by LovD to form lovastatin.