Dissecting endonuclease and exonuclease activities in endonuclease V from Thermotoga maritima

Endonuclease V is an enzyme that initiates a conserved DNA repair pathway by making an endonucleolytic incision at the 3'-side 1 nt from a deaminated base lesion. DNA cleavage analysis using mutants defective in DNA binding and Mn(2+) as a metal cofactor reveals a novel 3'-exonuclease activity in endonuclease V [Feng,H., Dong,L., Klutz,A.M., Aghaebrahim,N. and Cao,W. (2005) Defining amino acid residues involved in DNA-protein interactions and revelation of 3'-exonuclease activity in endonuclease V. Biochemistry, 44, 11486-11495.]. This study defines the enzymatic nature of the endonuclease and exonuclease activity in endonuclease V from Thermotoga maritima. In addition to its well-known inosine-dependent endonuclease, Tma endonuclease V also exhibits inosine-dependent 3'-exonuclease activity. The dependence on an inosine site and the exonuclease nature of the 3'-exonuclease activity was demonstrated using 5'-labeled and internally-labeled inosine-containing DNA and a H214D mutant that is defective in non-specific nuclease activity. Detailed kinetic analysis using 3'-labeled DNA indicates that Tma endonuclease V also possesses non-specific 5'-exonuclease activity. The multiplicity of the endonuclease and exonuclease activity is discussed with respect to deaminated base repair.