TABLE 1.
Specific exoribonucleolytic activity of wild-type and mutant enzymes
Exoribonucleolytic activity was assayed using a 35-nt poly(A) chain as substrate. Activity assays were performed in triplicate as described under “Experimental Procedures.” Each value represents nmol of substrate oligoribonucleotide consumed per min and per nmol of protein, and the exoribonucleolytic activity of the wild-type enzyme was taken as 100%.
| Protein | Protein activity | Relative activity |
|---|---|---|
| nmol min−1nmol−1 | % | |
| WT RNase II | 0.30 ± 0.04 | 100 |
| Y313F | 0.35 ± 0.04 | 117 |
| Y313A | <0.01 | 1 |
| E390A | 0.36 ± 0.03 | 120 |
| D201N | <0.01 | 0.2 |
| D201N/Y313F | <0.01 | <0.1 |
| D201N/E390A | 0.31 ± 0.06 | 103 |
| Y313F/E390A | 0.33 ± 0.01 | 110 |
| D210N/Y313F/E390A | ≪0.01 | ≪0.1 |
| E542A | 33.75 ± 3.90 | 11,250 |
| R500A | ≪0.01 | ≪0.1 |