Reaction mixtures (80 µl) containing 20 mM Tris-HCl (pH 7.5), 5 mM MgCl2, 0.5 mM (NH4)2PO4, 0.3 µM FL PNPase protomer, and 0.1 µM 5’ 32P-labeled 24-mer RNA with three, two or one internal deoxyribonucleotides (shown at bottom, with deoxys highlighted in gray) were incubated at 37°C. Aliquots (10 µl) were withdrawn at the times specified and quenched with formamide/EDTA. The reaction products were analyzed by urea-PAGE and visualized by autoradiography.