HMG-CoA reductase; part of the first module of ergosterol biosynthesis pathway that includes the early steps of the pathway, conserved across all eukaryotes, and which results in the formation of mevalonate from acetyl-coenzyme A (acetyl-CoA) (Probable). In this module, the cytosolic acetyl-CoA acetyltransferase catalyzes the formation of acetoacetyl-CoA (By similarity). The hydroxymethylglutaryl-CoA synthase then condenses acetyl-CoA with acetoacetyl-CoA to form HMG-CoA (By similarity). The rate-limiting step of the early module is the reduction to mevalonate by the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase hmgA (Probable). (R)-mevalonate + CoA + 2 NADP(+) = (3S)-hydroxy-3-methylglutaryl-CoA + 2 H(+) + 2 NADPH Metabolic intermediate biosynthesis; (R)-mevalonate biosynthesis; (R)-mevalonate from acetyl-CoA: step 3/3. Belongs to the HMG-CoA reductase family.