Acetyl-CoA acetyltransferase; 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) (PubMed:2900076). In this module, the acetyl-CoA acetyltransferase ERG10 catalyzes the formation of acetoacetyl-CoA (PubMed:2900076). The hydroxymethylglutaryl-CoA synthase ERG13 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) reductases HMG1 and HMG2 which are derived from a single ancestral HMGR gene by gene duplication (By similarity). 2 acetyl-CoA = acetoacetyl-CoA + CoA Metabolic intermediate biosynthesis; (R)-mevalonate biosynthesis; (R)-mevalonate from acetyl-CoA: step 1/3. Homotetramer. Belongs to the thiolase-like superfamily. Thiolase family.