Polynucleotide for modifying target sequence and use thereof

An isolated cell comprising:

• 1) A circular donor polynucleotide for modifying a genomic sequence of the isolated cell, wherein the circular donor polynucleotide comprises:
• a) a region homologous to the genomic sequence to be modified, wherein the homologous region comprises:
• i) one or more modification positions, wherein each modification position corresponds to a position in the genomic sequence to be modified, and the modification position in the homologous region has a different sequence from the corresponding position in the genomic sequence to be modified;
• and
• ii) a single cleavable site;
• and
• b) a linker polynucleotide linking both ends of the homologous region to each other, wherein the linker polynucleotide comprises a positive selection marker gene and a negative selection marker gene;
• and
• 2) A vector that expresses a restriction enzyme capable of cleaving the single cleavable site of the circular donor polynucleotide.