甾体类药物是应用广泛，仅次于抗生素的第二大药物。工业上利用微生物转化法生产甾体药物在经济、生态环保方面有巨大优势。虽然近两年以结核分枝杆菌为模型，研究了甾体代谢相关机理，但对具体酶反应详细机制、基因簇调控等尚待深入研究。负责甾体降解的基因一般呈基因簇（约100kb）形式排列且国际上已得到的基因簇很少，这增加了从基因簇水平研究甾体代谢的难度。目前甾体药物生产关键技术被一些大型跨国制药公司垄断。我国作为皂素资源与中低端甾体药物生产大国，虽工业规模大，但利润微薄，这严重制约行业的发展。本申请首先研究甾体代谢关键基因的表征及其分子机理，进而试图利用Fosmid文库得到基因簇全序列，并利用转录组分析挖掘基因簇上的基因信息，解析未知基因的功能。综上，本申请不仅在科学问题上研究甾体代谢基因簇的功能和调控机理，更为基因工程菌株的构建及基因工程在甾体药物生产中的应用乃至国内甾体医药工业发展及打下一定的基础。

Due to the significant physiological activity, steroid drugs have been widely used in clinic application as its second place following antibiotic drugs. In contrast to the chemical synthesis, biotransformation provides an alternative method in the production of steroid medicine intermediates and has been used extensively as a common and economical process in the pharmaceutical industry. Although，steroidal degradation mechanism has been researched using Mycobacterium tuberculosis as the mode bacteria, the detailed mechanism of sterol metabolism of key enzyme reactions and related regulation mechanism remains to be in-depth study. The gene responsible for the steroidal degradation general arranged as a gene cluster with the length about 100 kbp, and presently only a few steroidal degradation gene cluster were repoerted. This increases the difficulty to study the metabolism of the steroidal degradation gene cluster from the gene cluster level. In abroad, the key technologies of steroidal drugs production was monopolized by some large multinational pharmaceutical companies. As the main saponin resources and low-end steroidal drugs producing country, although steroidal pharmaceutical industry is a large scale, the profits is meager. Present domestic research of steroid production strains is just limited to strain isolation and mutation screening, but not involved in the steroid degradation genes at the molecular level, which hinder the development of domestic steroid drug industry. To solve the scientific issues, this application research the key gene in steroidal degradation gene cluster and the molecular mechanisms of the key gene in-depth research. Then, we try to get the gene cluster sequences using the method of building genomic fosmid library. And the genetic information of steroidal degradation gene cluster was researched using the methods of transcriptome analysis. In summary，this study not only research the function and regulation mechanism of steroidal degradation gene cluster but also provide a feasible way to achieve excellent phytosterol-transforming strains with high product purity. With the development of molecular biology and in-depth studies on steroid degradation system, genetic engineering is surely to play an important role in the production of steroid drugs and promote the development of domestic steroidal pharmaceutical industries.