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CeSchmitz committed Apr 18, 2024
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Expand Up @@ -5,19 +5,18 @@ Rapid Whole-Genome Identification of High Quality CRISPR Guide RNAs with the Cra

## Preamble

> The design of CRISPR-Cas9 guide RNAs is not trivial. In particular, evaluating the risk of off-target
modifications is computationally expensive: a brute-force approach would require comparing each candidate
guide with every possible CRISPR target site in the genome. In a mammalian genome, this means hundreds of
millions of comparisons for each guide. We have previously introduced Crackling, a gRNA design tool that
relies on Inverted Signature Slice Lists (ISSL) to accelerate off-target scoring by only considering sites
with partial matches (a slice) with the candidate guide. This produced an order of magnitude speed up whilst
still maintaining scoring accuracy. Here, we present a complete reimplementation of Crackling in C++ and
discuss further improvements. Using longer slices means fewer comparisons, and we show it is possible to
construct a collection of slices that still preserve an exact off-target score. We have benchmarked two ISSL
configurations with the new version of Crackling and report a 15-22 times speed up over the default ISSL
configuration. This increased performance comes at the cost of increased memory usage, but this can be offset
by using memory mapped files, and we show that this has no significant impact on performance.
CracklingPlusPlus is available at https://github.com/bmds-lab/CracklingPlusPlus under the Berkeley Software
> The design of CRISPR-Cas9 guide RNAs is not trivial. In particular, it is crucial to evaluate
the risk of unintended, off-target modifications, but this is computationally expensive. To
avoid a brute-force approach where each guide RNA is compared against every possible CRISPR
target site in the genome, we previously introduced Crackling, a guide RNA design tool that
relies on exact matches over 4bp subsequences to approximate a neighbourhood and accelerate
off-target scoring by greatly reducing the search space. While this was faster than other
existing tools, it still generates large neighbourhoods. Here, we aim to further reduce the
search space by requiring more, now non-contiguous, exact matches. The new implementation,
called Crackling++, is benchmarked against our initial approach and other off-target evaluation
tools. We show that it provides the fastest way to assess candidate guide RNAs. By using memorymapped
files, it also scales to the largest genomes.
Crackling++ is available at https://github.com/bmds-lab/CracklingPlusPlus under the Berkeley Software
Distribution (BSD) 3-Clause license.

## Dependencies
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