The principle of the method can be described as follows:
The target nucleotide sequence is conjoined with a protein-coding nucleotide sequence (in a vector system) and is expressed in host cells (E. coli).
If the gene of interest is intact, a complete fusion-protein is produced, which leads to death of the host cells (no colony formation).
If the target gene carries a mutation (i.e. stop- codon by a point mutation; frameshift mutations), no fusion-protein or a defective one is expressed, so the host cell survives and colonies are formed.

Gene segments changed by a mutation are indicated very easily by host cell growth. Another advantage is the possibility for further analysis of the grown host cells.

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