Almost complete sequence specific (1)H, (13)C and (15)N resonance assignments of a mutant of UV inducible transcript (S55A-UVI31+) from Chlamydomonas reinhardtii are reported, as a prelude to its structural and functional characterization. Site-directed mutagenesis of uvi31+ was carried out using complementary mutation harbouring oligonucleotides for S55A mutant. The resulting mutant was sequenced and then S55A mutant of uvi31+ cDNA were expressed in E. coli, and purification were carried out from where the protein was purified to high homogeneity. The point mutation S55A in UVI31+ results in a significant enhancement in its DNA endonuclease activity as compared to its wild type protein.