A new type of CRISPR has suppressed genes without cutting DNA.

An international team of genetic researchers has discovered how cells utilize a specific system to locate and suppress unwanted genes. In the future, this could lead to safer genetic editing capable of impacting defective genes that cause diseases.

“Unlike the well-known CRISPR system, often referred to as 'molecular scissors', the new type IV-A CRISPR does not cut genes. Instead, it employs an RNA-guided 'effector' complex to attract an enzyme called DinG, which moves along the DNA and suppresses the activity of target genes in a more gentle manner,” explained the lead researcher, Professor Patrick Pausch (Patrick Pausch).

The scientist noted that his team focused on the mechanism of precisely locating the DNA segment from which the system begins its work. To recognize a short constant sequence of amino acids or nucleotides, known as a motif, adjacent to the target DNA strand, the system utilizes two proteins: Cas8 and Cas5. When both proteins detect the desired motif, they unwind the DNA double helix and examine the target DNA region.

A key step in the verification process is the formation of R loops, which are open structures of DNA. Unlike intact DNA, R loops can bind RNA. This molecule already signals the system about the need to suppress the gene.

“All CRISPR-Cas systems that interact with DNA use R loops to recognize the target DNA region. Stable R loops are formed only in the presence of a DNA sequence that sufficiently matches the guiding RNA. The R loop essentially tells the system that it’s time to start suppressing the gene,” the professor explained.

The enzyme DinG, which is part of the IV-A CRISPR system, enhances the gene suppression process by unwinding the DNA strands. The action of the enzyme allows the developed tool to affect longer segments of DNA.

This new research provides a detailed description of the internal processes of DNA interference using the IV-A CRISPR method, suppressing gene expression (i.e., the coding of proteins synthesized by the organism) up to the transcription stage. Their work lays a structural foundation for developing genome editing tools using IV-A CRISPR. A scientific article on this topic has been published in the journal Nature Communications.

The CRISPR methods have ushered in a new era in genome editing, with expectations for a rapid revolution in genetic engineering. However, many errors still occur during the DNA cutting stage. This limits the utility of the method in creating new resilient agricultural crops. The IV-A CRISPR developed by geneticists offers more opportunities for genetic engineering as it works with DNA in a less invasive manner.