3 - RNase T1/RNase T2 Family RNases

Abstract

This chapter provides an overview of RNase T1/RNase T2 family RNases. The chapter begins with a discussion on the structure of RNase T1 family RNases. RNase T1 is known to be a guanylic acid-specific RNase and its molecular weight is around 11,000. The RNase T1 family RNases are divided into two subfamilies according to their sequences. One is the RNase T1 subfamily (typified by RNase T1) and the other is the barnase subfamily. The latter includes RNase Sa, RNase St, RNase Bi, and barnase. The RNases of the RNase T1 subfamily are divided into five groups according to the location of the disulfide bond. The most common group is represented by RNase T1, which has two disulfide bonds, between Cys-2 and Cys-10 and between Cys-6 and Cys-103 (RNase T1 numbering). This chapter explains concepts related to mechanism of action of RNase T1 family RNases. It also describes and identification of active site amino acid residues. It explains determination of active site amino acids by protein engineering. An overview of amino acid residues responsible for catalysis is presented. The chapter elaborates in detail about mechanism of hydrolysis of nucleotidyl bonds by RNase Rh. The chapter concludes with a discussion on base preference of RNase Rh.