2, 3-Oxidosqualene, an intermediate produced by the ergosterol biosynthetic pathway in Saccharomyces ceravisiae, is the precursor of triterpenoids.The metabolic flow from 2, 3-oxidosqualene to ergosterol is needed to be downregulated when S.cerevisiae is used as a host to build a metabolic pathway of triterpenoids by synthetic biotechnology.Lanosterol synthase (erg7) catalyzes the first step from 2, 3-oxidosqualene to ergosterol in S.cerevisiae.So the downregulation of erg7 gene expression was studied by gene knockout and antisense RNA technology in this research.