@article {1017, title = {Substrate specificity and kinetic framework of a DNAzyme with an expanded chemical repertoire: a putative RNaseA mimic that catalyzes RNA hydrolysis independent of a divalent metal cation}, journal = {Nucleic Acids Research}, volume = {32}, number = {22}, year = {2004}, note = {ISI Document Delivery No.: 887METimes Cited: 24Cited Reference Count: 71}, pages = {6660-6672}, type = {Article}, abstract = {This work addresses the binding, cleavage and dissociation rates for the substrate and products of a synthetic RNaseA mimic that was combinatorially selected using chemically modified nucleoside triphosphates. This trans-cleaving DNAzyme, 9(25)-11t, catalyzes sequence-specific ribophosphodiester hydrolysis in the total absence of a divalent metal cation, and in low ionic strength at pH 7.5 and in the presence of EDTA. It is the first such sequence capable of multiple turnover. 9(25)-11t consists of 31 bases, 18 of which form a catalytic domain containing 4 imidazole and 6 allylamino modified nucleotides. This sequence cleaves the 15 nt long substrate, S1, at one embedded ribocytosine at the eighth position to give a 5{\textquoteright}-product terminating in a 2{\textquoteright},3{\textquoteright}-phosphodiester and a 3{\textquoteright}-product terminating in a 5{\textquoteright}-OH. Under single turnover conditions at 24degreesC, 9(25)-11t displays a maximum first-order rate constant, k(cat), of 0.037 min(-1) and a catalytic efficiency, k(cat)/K-m, of 5.3 x 10(5) M-1 min(-1). The measured value of k(cat) under catalyst excess conditions agrees with the value of k(cat) observed for steady-state multiple turnover, implying that slow product release is not rate limiting with respect to multiple turnover. The substrate specificity of 9(25)-11t was gauged in terms of k(cat) values for substrate sequence variants. Base substitutions on the scissile ribose and at the two bases immediately downstream decrease k(cat) values by a factor of 4 to 250, indicating that 9(25)-11t displays significant sequence specificity despite the lack of an apparent Watson-Crick base-pairing scheme for recognition.}, keywords = {CATIONS, CLEAVING DNA ENZYME, CYTOSOLIC FREE MAGNESIUM, HAIRPIN RIBOZYME CLEAVAGE, HAMMERHEAD, IMIDAZOLYL FUNCTIONALITIES, IN-VITRO SELECTION, MONOVALENT, NUCLEIC-ACIDS, NUCLEOSIDE TRIPHOSPHATES, SEQUENCE-SPECIFIC CLEAVAGE}, isbn = {0305-1048}, url = {://000226309400036}, author = {Ting, R. and Thomas, J. M. and Lermer, L. and Perrin,David M.} }