In addition to NTPase and dATPase activity, rNSs also exhibited the nucleic acid 59 phosphatase activity (Fig. 6A ) that was inhibited by AMP (Fig. 6B) . The rNSs could remove the 59 Phosphate from ssRNA (Fig. 6A) , ssDNA, dsDNA and dsRNA (Fig. 7A, B and D) . However, it failed to remove the phosphate from siRNA in which the 59 end is recessed (Fig. 7C) . The 59 a Phosphatase activity of rNSs was inhibited by ATP. It is possible that ATP acts as the competitor for the binding of the substrate. Interestingly, K189A mutant which was completely inactive as far as the ATPase activity was concerned, was fully active and could remove the 59 phosphate from 59 end of the nucleic acid (Fig. 6C) . As mentioned earlier, the lysine in the GKT motif is involved in the binding of b, c phosphate for positioning and cleavage of c phosphate. However, the rNSs removes the a phosphate from the 59 end labelled nucleic acid. Therefore, the mutation K189 to A did not result in loss of 59 phosphatase activity. In the D159A mutant, only a partial decrease (20%) in activity was observed for 59 phosphatase activity suggesting that this reaction could also be metal ion dependent.