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) (By similarity). HMG1 catalyzes the reduction of hydroxymethylglutaryl-CoA (HMG-CoA) to mevalonate (By similarity). The first module starts with the action of the cytosolic acetyl-CoA acetyltransferase ERG10 that catalyzes the formation of acetoacetyl-CoA. The hydroxymethylglutaryl-CoA synthase ERG13 then condenses acetyl-CoA with acetoacetyl-CoA to form HMG-CoA. The 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase HMG1 finally reduces HMG-CoA to produce mevalonate (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. Expression is not affected by lovastatin or fluconazole. Belongs to the HMG-CoA reductase family.