FIGURE 3.

Exoribonuclease activity with ds16–30 substrate; comparison of wild-type and mutant proteins. Activity assays were performed as described under “Experimental Procedures” using a 30-mer oligoribonucleotide hybridized to the complementary 16mer oligodeoxyribonucleotide, thus obtaining the corresponding double-stranded substrate 16–30ds. The mutants used and their respective protein concentrations are shown. The wild-type enzyme was used as control. Samples were taken during the reaction at the time points indicated, and reaction products were analyzed in a 20% polyacrylamide, 7 m urea gel. Control reactions with no enzyme added (Ctrl) were incubated at the maximum reaction time for each protein. Length of substrates and degradation products are indicated in the figure.