Method for increasing the efficiency of double-strand-break induced mutagenesis

A method for increasing double-strand-break induced mutagenesis at a genomic locus of interest in a cell comprising the steps of:

• (i) identifying at said genomic locus of interest at least one DNA target sequence cleavable by one natural or engineered rare-cutting endonuclease;
• (ii) expressing said rare-cutting endonuclease in the cell together with a polynucleotide encoding a fusion protein that comprises:
• a first polypeptide that is a human TREX2 exonuclease protomer of SEQ ID NO:
• 26 or functional mutant thereof that shares at least 80% identity with the human TREX2 exonuclease protomer;
• a second polypeptide that is a human TREX2 exonuclease protomer of SEQ ID NO:
• 26 or functional mutant thereof that shares at least 80% identity with the human TREX2 exonuclease protomer;
• and
• a peptidic linker connecting said first and second polypeptides;
• (iii) thereby obtaining, by expression of said fusion protein in said cell, increased double strand-break-induced mutagenesis at said genomic locus of interest.