Guide RNAs containing universal bases enable Cas9/Cas12a recognition of polymorphic sequences

Genetic variance poses a major challenge for CRISPR-based human therapeutics and pathogen diagnostics. Here the authors show how to circumvent this issue by using guide RNAs containing universal bases to tailor Cas9/Cas12 specificity. CRISPR/Cas complexes enable precise gene editing in a wide variety of organisms. While the rigid identification of DNA sequences by these systems minimizes the potential for off-target effects, it consequently poses a problem for the recognition of sequences containing naturally occurring polymorphisms. The presence of genetic variance such as single nucleotide polymorphisms (SNPs) in a gene sequence can compromise the on-target activity of CRISPR systems. Thus, when attempting to target multiple variants of a human gene, or evolved variants of a pathogen gene using a single guide RNA, more flexibility is desirable. Here, we demonstrate that Cas9 can tolerate the inclusion of universal bases in individual guide RNAs, enabling simultaneous targeting of polymorphic sequences. Crucially, we find that specificity is selectively degenerate at the site of universal base incorporation, and remains otherwise preserved. We demonstrate the applicability of this technology to targeting multiple naturally occurring human SNPs with individual guide RNAs and to the design of Cas12a/Cpf1-based DETECTR probes capable of identifying multiple evolved variants of the HIV protease gene. Our findings extend the targeting capabilities of CRISPR/Cas systems beyond their canonical spacer sequences and highlight a use of natural and synthetic universal bases.

Automated summary

The use of guide RNAs containing universal bases can enhance the specificity of CRISPR-based gene editing and pathogen diagnostics, overcoming the challenge of genetic variance. The introduction of universal bases allows for simultaneous targeting of polymorphic sequences by Cas9/Cas12, extending the targeting capabilities of CRISPR/Cas systems.