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Introduction of mismatches in a random shRNA-encoding library improves potency for phenotypic selection.

ABSTRACT: RNA interference (RNAi) is a mechanism for interfering with gene expression through the action of small, non-coding RNAs. We previously constructed a short-hairpin-loop RNA (shRNA) encoding library that is random at the nucleotide level [1]. In this library, the stems of the hairpin are completely complementary. To improve the potency of initial hits, and therefore signal-to-noise ratios in library screening, as well as to simplify hit-sequence retrieval by PCR, we constructed a second-generation library in which we introduced random mismatches between the two halves of the stem of each hairpin, on a random template background. In a screen for shRNAs that protect an interleukin-3 (IL3) dependent cell line from IL3 withdrawal, our second-generation library yielded hit sequences with significantly higher potencies than those from the first-generation library in the same screen. Our method of random mutagenesis was effective for a random template and is likely suitable, therefore, for any DNA template of interest. The improved potency of our second-generation library expands the range of possible unbiased screens for small-RNA therapeutics and biologic tools.

SUBMITTER: Wang Y

PROVIDER: S-EPMC3911983 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Localized sets of random point mutations generated by PCR amplification can be transferred efficiently to the chromosome of Acinetobacter ADP1 (also known as strain BD413) by natural transformation. The technique does not require cloning of PCR fragments in plasmids: PCR-amplified DNA fragments are internalized by cells and directly incorporated into their genomes by homologous recombination. Previously such procedures for random mutagenesis could be applied only to Acinetobacter genes affording the selection of mutant phenotypes. Here we describe the construction of a vector and recipient that allow for mutagenesis, recovery, and expression of heterologous genes that may lack a positive selection. The plasmid carries an Acinetobacter chromosomal segment interrupted by a multiple cloning site next to a kanamycin resistance marker. The insertion of heterologous DNA into the multiple cloning site prepares the insert as a target for PCR mutagenesis. PCR amplifies the kanamycin resistance marker and a flanking region of Acinetobacter DNA along with the insert of heterologous DNA. Nucleotide sequence identity between the flanking regions and corresponding chromosomal segments in an engineered Acinetobacter recipient allows homologous recombination of the PCR-amplified DNA fragments into a specific chromosomal docking site from which they can be expressed. The recipient strain contains only a portion of the kanamycin resistance gene, so donor DNA containing both this gene and the mutagenized insert can be selected by demanding growth of recombinants in the presence of kanamycin. The effectiveness of the technique was demonstrated with the relatively GC-rich Pseudomonas putida xylE gene. After only one round of PCR amplification (35 cycles), donor DNA produced transformants of which up to 30% carried a defective xylE gene after growth at 37 degrees C. Of recombinant clones that failed to express xylE at 37 degrees C, about 10% expressed the gene when grown at 22 degrees C. The techniques described here could be adapted to prepare colonies with an altered function in any gene for which either a selection or a suitable phenotypic screen exists.

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Introduction of mismatches in a random shRNA-encoding library improves potency for phenotypic selection.

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