Interaction of VspI and Tru9I restriction endonucleases with synthetic oligonucleotides

We describe the properties of two new restriction endonucleases VspI and Tru9I which recognize sequences AT TAAT and T TAA, respectively. The molecular weights, subunit structure and steady-state kinetic constants of these enzymes for native and modified substrates have been determined. We have investigated the interaction of VspI and Tru9I with synthetic oligonucleotides containing modifications either within the recognition sites or around them. These modifications represent the substitution of different DNA deoxyribonucleosides by 1,2-dideoxy-D-ribofuranose, which corresponds to loss of the heterocyclic base while the sugar-phosphate chain remains intact. The effects of the substitutions were analyzed by determining the steady-state kinetic values of the hydrolysis reaction by VspI and Tru9I. The enzymes exhibited Michaelis-Menten kinetics for hydrolyzable substrates. The initial rates (V0) of hydrolysis of modified and unmodified strands of the duplexes varied as a result of these substitutions. The substrates for VspI and Tru9I which contain modifications around the bond to be hydrolyzed or within the complementary nucleosides were unreactive.