Mammalian cells are widely used for the production of therapeutic recombinant proteins, as these cells facilitate accurate folding and post-translational modifications often essential for optimum activity. Targeted insertion of a plasmid harboring a gene of interest into the genome of mammalian cells for the expression of a desired protein is a key step in production of such biologics. Here we show that a site specific double strand break (DSB) generated both in the genome and the donor plasmid using the CRISPR-Cas9 system can be efficiently used to target ∼5 kb plasmids into mammalian genomes via nonhomologous end joining (NHEJ). We were able to achieve efficiencies of up to 0.17% in HEK293 cells and 0.45% in CHO cells. This technique holds promise for quick and efficient insertion of a large foreign DNA sequence into a predetermined genomic site in mammalian cells.

The complex formed between the U2 and U6 small nuclear (sn)RNA molecules of the eukaryotic spliceosome plays a critical role in the catalysis of precursor mRNA splicing. Here, we have used enzymatic structure probing, 19 F NMR, and analytical ultracentrifugation techniques to characterize the fold of a protein-free biophysically tractable paired construct representing the human U2-U6 snRNA complex. Results from enzymatic probing and 19 F NMR for the complex in the absence of Mg 2+ are consistent with formation of a four-helix junction structure as a predominant conformation. However,19 F NMR data also identify a lesser fraction (up to 14% at 25°C) of a three-helix conformation. Based upon this distribution, the calculated ΔG for interconversion to the four-helix structure from the three-helix structure is approximately −4.6 kJ/mol. In the presence of 5 mM Mg 2+ , the fraction of the three-helix conformation increased to ∼17% and the Stokes radius, measured by analytical ultracentrifugation, decreased by 2%, suggesting a slight shift to an alternative conformation. NMR measurements demonstrated that addition of an intron fragment to the U2-U6 snRNA complex results in displacement of U6 snRNA from the region of Helix III immediately 5 ′ of the ACAGAGA sequence of U6 snRNA, which may facilitate binding of the segment of the intron adjacent to the 5 ′ splice site to the ACAGAGA sequence. Taken together, these observations indicate conformational heterogeneity in the protein-free human U2-U6 snRNA complex consistent with a model in which the RNA has sufficient conformational flexibility to facilitate inter-conversion between steps of splicing in situ.

RNA molecules play an essential role in biology. In addition to transmitting genetic information, RNA can fold into unique tertiary structures fulfilling a specific biologic role as regulator, binder or catalyst. Information about tertiary contact formation is essential to understand the function of RNA molecules. Hydroxyl radicals (•OH) are unique probes of the structure of nucleic acids due to their high reactivity and small size. 1 When used as a footprinting probe, hydroxyl radicals map the solvent accessible surface of the phosphodiester backbone of DNA 1 and RNA 2 with as fine as single nucleotide resolution. Hydroxyl radical footprinting can be used to identify the nucleotides within an intermolecular contact surface, e.g. in DNA-protein 1 and RNA-protein complexes. Equilibrium 3 and kinetic 4 transitions can be determined by conducting hydroxyl radical footprinting as a function of a solution variable or time, respectively. A key feature of footprinting is that limited exposure to the probe (e.g., 'single-hit kinetics') results in the uniform sampling of each nucleotide of the polymer. 5

RNA molecules play an essential role in biology. In addition to transmitting genetic information, RNA can fold into unique tertiary structures fulfilling a specific biologic role as regulator, binder or catalyst. Information about tertiary contact formation is essential to understand the function of RNA molecules. Hydroxyl radicals (•OH) are unique probes of the structure of nucleic acids due to their high reactivity and small size. 1 When used as a footprinting probe, hydroxyl radicals map the solvent accessible surface of the phosphodiester backbone of DNA 1 and RNA 2 with as fine as single nucleotide resolution. Hydroxyl radical footprinting can be used to identify the nucleotides within an intermolecular contact surface, e.g. in DNA-protein 1 and RNA-protein complexes. Equilibrium 3 and kinetic 4 transitions can be determined by conducting hydroxyl radical footprinting as a function of a solution variable or time, respectively. A key feature of footprinting is that limited exposure to the probe (e.g., 'single-hit kinetics') results in the uniform sampling of each nucleotide of the polymer. 5 In this video article, we use the P4-P6 domain of the Tetrahymena ribozyme to illustrate RNA sample preparation and the determination of a Mg(II)-mediated folding isotherms. We describe the use of the well known hydroxyl radical footprinting protocol that requires H2O2 (we call this the 'peroxidative' protocol) and a valuable, but not widely known, alternative that uses naturally dissolved O2 (we call this the 'oxidative' protocol). An overview of the data reduction, transformation and analysis procedures is presented.