Squalene synthase catalyzes the condensation of two molecules of farnesyl diphosphate to produce squalene,the first committed precusor for sterol,brassinosteroid,and triterpene biosynthesis.A squalene synthase gene,designated IoSQS,was isolated from Inonotus obliquus,a medicinal mushroom produces a plethora of bioactive triterpenes.The IoSQS cDNA was found to contain an open reading frame of 1,476 bp,encoding a protein of 491 amino acids with a calculated molecular mass of 55.85 kDa.The IoSQS genomic DNA sequence consisted of 1,813 bp and contained four exons and three introns.The restriction fragment polymorphisms revealed by Southern blot analysis suggested that IoSQS was a single copy gene.