Ribonucleases A and T1 Comparable Mechanisms of RNA Cleavage with Different Active Site Geometries

Abstract

There are a variety of enzymes which cleave the phosphodiester link in ribo- and deoxyribonucleic acids. They exhibit different catalytic activities, different mechanisms of cleavage, and different three-dimensional structures. The best known examples are DNase I which acts upon single and double stranded DNA , staphylococcal nuclease which cleaves P-0 bonds in RNA and DNA single strands2 , and the two RNases A and T1 which cut at the 3′-end of pyrimidine and guanosine nucleotides respectively3-5 . Although the two RNases have different molecular topology, the mechanism of hydrolysis is similar and suggestive of a comparable active site geometry. Since high resolution crystal structures are available (1.5A for RNase A and 2.oA for RNase T1)3-5, a study of the arrangement of the functional amino acids in the1 active sites of the two enzymes is of interest.