Image from Lukas Kummer
iGEM Project 2023 | Part 6
Genome editing is an extremely precise procedure of gene modification based on targeted mutagenesis. Until the 80s of the last century, DNA editing was a long and complex technique, and basic knowledge was still very limited. This procedure uses different types of nucleases that can act towards any sequence, the most innovative strategy introduced in the last years is the CRISPR/Cas. This system was originally identified within many bacteria, present as an adaptive immunity and defense mechanism to counter viral infections carried out by bacteriophages, the viruses of bacteria.
Cas is a protein produced by the bacteria which recognise the non-self DNA introduced by the virus and cut it into small pieces, making it unreadable by the enzymes responsible for protein synthesis and thus harmless. In this way, the genes of the viral genome will not be translated into proteins by the cell machinery of the bacteria, so the virus particles will not be produced. However, the Cas protein has another function which is creating an immunological memory. One fragment of the viral DNA is integrated into the bacterial genome in a specific region named CRISPR locus. This procedure repeats for every molecule recognised as non-self DNA, building a series of short sequences integrated one after another in the CRISPR locus, separated from even shorter and identical sequences of bacterial DNA. CRISPR indeed stands for Clustered Regularly Interspersed Palindromic Repeats, small bacterial DNA pieces separating the different viral fragments integrated in the genome.
But how does the Cas protein distinguish between bacterial and extracellular DNA? We will explain it in the next article. Stay tuned!