With arsenic pollution in the environment in mind, this project will focus on the biotransformation of arsenic (arsenate reduction, arsenite methylation and volatilization of organic arsenic). The role and mechanism of algae in arsenic biotransformation will be studied, with special interest given to the protein function-structure relationship on the molecular level. The main aims of this project includes: (1)the cloning and functional studies of key genes involved in arsenic biotransformation in model algae: Based on the physilogical data, arsenate reductase and arsenic methyltransferase genes will be cloned from model algae’s genomes. These genes will then be expressed in E. coli and their function will be studied; (2)the expression, purification, and crystal structural studies of the proteins involved in arsenic biotransformation in model algae. The function-structure relationship will be studied, thus making the structure-based genetic engeneering possible. This project is of significance for studying algae’s role in arsenic biogeochemistry, fate, and toxicity. The research on arsenic volatilization, especially its molecular mechanism and structural basis, is just emerging and novel.