basic amino acids and aromatic amino acids between amino acid 128 to 137 positions the specific activity of the enzyme is greatly increased at low salt concentrations when substitutions are made in aromatic amino acids in the carboxy terminal region application_number US 82750692 A description in accordance with the present invention a t4 endonuclease v dna repair enzyme includes an amino acid sequence including a carboxyl terminal region for pyrimidine dimer binding of a specific activity the sequence of the t4 endonuclease v gene denv and coded for amino acids is given in table 4 valerie k et al identification physical map location and sequence of the denv gene from bacteriophage t4 nucleic acid res 12 8085 8096 1984 the carboxyl terminal region of the endonuclease v enzymes spans trp 128 to tyr 137 trp tyr lys tyr tyr gly lys ala ile tyr the c terminal region of endonuclease v enzyme is capable of binding the kinked partially single stranded dna at the site of a pyrimidine dimer the present invention is based on studies showing the terminal region including substitutions of other less polar aromatic amino acids increases the specific activity of the enzyme at low salt concentrations more specifically in accordance with the present invention aromatic amino acid substitutions phe 129 trp 129 for a more polar aromatic amino acid tyr 129 at the terminal region increases the specific activity of the endonuclease enzyme in accordance with the following experimental evidence mutant enzymes including substitutions tyr 129 u2192 phe sequence id nos 1 and 2 and tyr 129 u2192 trp sequence id nos 3 and 4 displayed a 1000 and 500 enhanced specific nicking activity respectively these reactions were also shown to be completely processive assays performed at higher.