Basic principle: CRISPR cluster is a special family of DNA repeats, which widely exists in the genomes of bacteria and archaea. Its sequence consists of a leading sequence, several short and highly conservative repetitive sequences and several spacer regions.

The leader region is generally located in the upstream of CRISPR cluster, which is an AT-rich region with a length of 300 ~ 500 BP, and is considered as the promoter sequence of CRISPR cluster. The length of the repetitive sequence region is 2 1 ~ 48bp, which contains palindromes and can form a hairpin structure.

The forms of gene editing technology are:

1, homologous recombination

Homologous recombination is the earliest technical method used to edit cell genome. Homologous recombination is the exchange (recombination) of genetic information between two similar (homologous) DNA strands.

2. Nuclease

The key of gene editing is to create DSB at a specific site in the genome. Commonly used restriction endonucleases are effective for DNA cleavage, but they are usually multi-site recognition cleavage with poor specificity. To solve this problem and create a DSB at a specific site.