Project description:These E. coli strains were grown with various signaling molecules and the expression profiles were determined. Keywords: addition of quorum and host hormone signals
Project description:CRISPR–Cas9 screening relies on uniform representation of single-guide RNA (sgRNA) libraries to enable accurate gene discovery. However, technical biases during library preparation can compromise screen performance. Here we show that commonly used “all-in-one” CRISPR vectors expressing both Cas9 and sgRNAs drive unintended Cas9 protein expression in Escherichia coli during plasmid amplification. This bacterial Cas9 expression causes guide-specific toxicity, leading to selective loss of sgRNAs and highly skewed library representation. We demonstrate that this effect occurs across multiple bacterial strains and affects both targeted and genome-wide libraries, including widely used human CRISPR libraries. Mechanistically, toxicity is driven by Cas9 expression rather than plasmid size and is only partially alleviated by catalytically inactive Cas9. Importantly, replacing the EF-1α promoter with a mouse phosphoglycerate kinase promoter suppresses Cas9 expression in bacteria while preserving genome editing efficiency in mammalian cells and restoring sgRNA uniformity. These findings identify a previously unrecognized source of bias in CRISPR library preparation and provide a practical solution to improve screening fidelity.
Project description:CRISPR–Cas9 screening relies on uniform representation of single-guide RNA (sgRNA) libraries to enable accurate gene discovery. However, technical biases during library preparation can compromise screen performance. Here we show that commonly used “all-in-one” CRISPR vectors expressing both Cas9 and sgRNAs drive unintended Cas9 protein expression in Escherichia coli during plasmid amplification. This bacterial Cas9 expression causes guide-specific toxicity, leading to selective loss of sgRNAs and highly skewed library representation. We demonstrate that this effect occurs across multiple bacterial strains and affects both targeted and genome-wide libraries, including widely used human CRISPR libraries. Mechanistically, toxicity is driven by Cas9 expression rather than plasmid size and is only partially alleviated by catalytically inactive Cas9. Importantly, replacing the EF-1α promoter with a mouse phosphoglycerate kinase promoter suppresses Cas9 expression in bacteria while preserving genome editing efficiency in mammalian cells and restoring sgRNA uniformity. These findings identify a previously unrecognized source of bias in CRISPR library preparation and provide a practical solution to improve screening fidelity.
2026-03-17 | GSE324351 | GEO
Project description:SLALOM: A Simple and Rapid Method for Enzymatically Generating CRISPR-Cas9 sgRNA Libraries
Project description:In this study we generated 5'P libraries in wt and RNAse III mutant strains, grown to exponential and stationary phases. Libraries that retain short RNA fragments were also generated in both growth phases. After sequencing by Illumina NextSeq 500 system, reads were mapped to E. coli genome NC_000913.3. By comparing the read start counts per position in the wt and mutant strain libraries we identified the cleavage sites of RNase III.
Project description:Increasing numbers of small proteins with diverse physiological roles are being identified and characterized in both prokaryotic and eukaryotic systems, but the origins and evolution of these proteins remain unclear. Recent genomic sequence analyses in several organisms suggest that new functions encoded by small open reading frames (sORFs) may emerge de novo from noncoding sequences. However, experimental data demonstrating if and how randomly generated sORFs can confer beneficial effects to cells are limited. Here we show that by up-regulating hisB expression, de novo small proteins (≤ 50 amino acids in length) selected from random sequence libraries can rescue Escherichia coli cells that lack the conditionally essential SerB enzyme. The recovered small proteins are hydrophobic and confer their rescue effect by binding to the 5’ end regulatory region of the his operon mRNA, suggesting that protein binding promotes structural rearrangements of the RNA that allow increased hisB expression. This study adds RNA regulatory elements as another interacting partner for de novo proteins isolated from random sequence libraries, and provides further experimental evidence that small proteins with selective benefits can originate from the expression of nonfunctional sequences.