含硫胺基酸如半胱胺酸與甲硫胺酸，對於生物细胞的正常生理具有重要的角色。硫酸鹽同化途徑，乃 將無機氧化態硫素，經由一系列的還原步驟，同化合成含硫胺基酸。本研究之目的，在探討人體病原 真菌隱球菌基因的生理功能與角色，利用體外轉位反應製備得到突變載體，以基因槍轉殖技術 進行基因轉殖，經南方雜合分析及細胞内硫離子含量測定，確認隱球菌met5突變株。性狀分析發現， met5突變株造成半胱胺酸營養缺陷型、生長速率緩慢、生殖菌絲減少、無黑色素形成，以及在替代性 昆蟲宿主接種試驗中，呈現致病力大幅下降等情形。上述met5突變株的缺陷，在重新轉殖MET5基因 至突變株後，皆回復至野生株之性狀。本研究之結果證實，硫酸鹽同化途徑對於隱球菌的營養需求具 有相當之重要性，而基因亦具有調控其他生理之角色。

Sulfur-containing amino acids such as cysteine and methionine are important for cellular physiology. Sulfate assimilation pathway (SAP) is a reduction sequence involved in the biosynthesis of these amino acids from the inorganic oxidized sulfur source. In this report, we studied the roles of the MET5 homologue in the human fungal pathogen Cryptococcus neoformans. The gene disruption construct was created by in vitro transposition and delivered into the wild-type strain by biolistic transformation. Gene disrupted mutants were verified and characterized. C. neoformans met5 mutants were auxotrophic for cysteine, impaired for growth, and severely attenuated for mating differentiation. The met5 mutants also failed to produce melanin and lost virulence in the alternative insect host model. All the defects were reverted to the wild-type by reintroduction of the intact copy MET5 gene. Consistent with previous reports, our results showed that the components of SAP are important for nutritional requirement and Met5 also plays additional roles in other physiological processes in C. neoformans.