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) (Ref.6). Erg10B catalyzes the formation of acetoacetyl-CoA from acetyl-CoA (Ref.6). The first module starts with the action of the cytosolic acetyl-CoA acetyltransferase erg10B that catalyzes the formation of acetoacetyl-CoA. The hydroxymethylglutaryl-CoA synthases erg13A and erg13B then condense 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. Mevalonate is also a precursor for the extracellular siderophore triacetylfusarinine C (TAFC) (PubMed:16110826, PubMed:22106303) (Probable). 2 acetyl-CoA = acetoacetyl-CoA + CoA Activity is increased by monovalent cations such as K(+), Rb(+) or Cs(+). Metabolic intermediate biosynthesis; (R)-mevalonate biosynthesis; (R)-mevalonate from acetyl-CoA: step 1/3. Homotetramer. Leads to lethality. Even though it is not involved in catalysis directly, the Cl(-) anion stabilizes the catalytic site via both direct and water-mediated hydrogen bonds to catalytic residues and residues adjacent. Belongs to the thiolase-like superfamily. Thiolase family.