Purine N7 groups that are crucial to the interaction of Escherichia coli RNase P RNA with tRNA

RNase P RNA that are important for tRNA binding under moderate salt conditi ons (0.1 M Mg2+, 0.1 M NH4+). The majority of identified positions represen t highly or universally conserved nucleotides, Our assay system allowed us, for the first time, to identify c7-deaza interference effects at two G res idues (G292, G306), Several c7-deazaadenine interference effects (A62, A65, A136, A249, A334, A351) have also been identified in other studies perform ed at very different salt concentrations, either selecting for substrate bi nding in the presence of 0.025 M Ca2+ and 1 M NH4+ or self-cleavage of a pt RNA-RNase P RNA conjugate in the presence of 3 M NH4+ or Na+. This indicate s that these N7 functional groups play a key role in the structural organiz ation of ribozyme-substrate and -product complexes, We further observed tha t a c7-deaza modification at A(76) Of tRNA interferes with tRNA binding to and ptRNA processing by E. coli RNase P RNA. This finding combined with the strong c7-deaza interference at G292 of RNase P RNA supports a model in wh ich substrate and product binding to E. coli RNase P RNA involves the forma tion of intermolecular base triples (A258-G292-C-75 and G291-G259-A(76)).