Enzymatic capture of an extrahelical thymine in the search for uracil in DNA

The enzyme uracil DNA glycosylase (UNG) excises unwanted uracil bases in the genome using an extrahelical base recognition mechanism. Efficient removal of uracil is essential for prevention of C-to-T transition mutations arising from cytosine deamination, cytotoxic U*A pairs arising from incorporation of dUTP in DNA, and for increasing immunoglobulin gene diversity during the acquired immune response. A central event in all of these UNG-mediated processes is the singling out of rare U*A or U*G base pairs in a background of approximately 10(9) T*A or C*G base pairs in the human genome. Here we establish for the human and Escherichia coli enzymes that discrimination of thymine and uracil is initiated by thermally induced opening of T*A and U*A base pairs and not by active participation of the enzyme. Thus, base-pair dynamics has a critical role in the genome-wide search for uracil, and may be involved in initial damage recognition by other DNA repair glycosylases.     

中美经济管理类教育的比较研究

分别对中美两国大学生、中国的60家大中型企业进行了问卷调查，对调查结果进行统计分析，揭示了中美两国经济管理类大学教育在创新性、有用性、互动性、努力程度、教学重点等5个方面的差异，得出了中国经济管理类大学本科教育的优势和不足。比较了中国与美国在经济管理类的大学教育，分析了中国劳务市场对大学毕业生的素质和能力的要求。