HYDROLYSIS OF A SLOW CYCLIC THIOPHOSPHATE SUBSTRATE OF RNASE T1 ANALYZED BY TIME-RESOLVED CRYSTALLOGRAPHY

Here we present a time-resolved crystallographic analysis of the hydro lysis of exo (Sp) guano sine 2',3'-cyclophosphorothioate by RNase T1. The use of a slow substrate and fast crystallization methods made it p ossible to perform the study with conventional data-collection techniq ues. The results support the idea that the hydrolysis reaction proceed s through a mechanism that is the inverse of the transesterification r eaction. In addition, the structures provide an explanation for the di fferential behavior of RNase T1 towards exo- and endo-cyclic thiophosp hates.