Expression of nicotiana glutinosa ribonucleases in escherichia coli

We previously isolated from Nicotiana glutinosa leaves three distinct cDNA clones, NGR1, NGR2, and NGR3, encoding a wound-inducible RNase NW, and putative RNases NGR2 and NGR3, respectively. In this study, we produced RNases NW and NGR3 in Escherichia coli and purified them to homogeneity. RNase NGR3 had non-absolute specificity toward polynucleotides, although RNase NW preferentially cleaved polyinosinic acid (Poly I). Both RNases NW and NGR3 were more active toward diribonucleoside monophosphates ApG, CpU, and GpU. Furthermore, kinetic parameters for RNase NW (K_m, 0.778 mM and k_cat, 1938 min⁻¹) and RNase NGR3 (K_m, 0.548 mM and k_cat, 408 min⁻¹) were calculated using GpU as a substrate.