HMG-CoA reductase; part of the first module of ergosterol biosynthesis pathway constitutes by the early steps of the pathway, conserved across all eukaryotes, and which results in the formation of mevalonate from acetyl-coenzyme A (acetyl-CoA) (PubMed:3065625, PubMed:3526336). HMG1 and HMG2 catalyze the reduction of hydroxymethylglutaryl-CoA (HMG-CoA) to mevalonate that is the rate-limiting step within the first mosule (PubMed:3526336). 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 rate-limiting step of the early module is the reduction to mevalonate by the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductases HMG1 and HMG2 which are derived from a single ancestral HMGR gene by gene duplication (PubMed:32679672). (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. The sterol-sensing domain (SSD) is required for sterol pathway signals to stimulate hmg2 ER-associated degradation and detects both geranylgeranyl pyrophosphate and a secondary oxysterol signal. When both HMG1 and HMG2 are deleted, cells are unable to undergo spore germination and vegetative growth. Belongs to the HMG-CoA reductase family.