T7 RNA polymerase transcription complex: what you see is not what you get

In-Cell Stability Prediction of RNA/DNA Hybrid Duplexes for Designing Oligonucleotides Aimed at Therapeutics

In cells, the formation of RNA/DNA hybrid duplexes regulates gene expression and modification. The environment inside cellular organelles is heterogeneously crowded with high concentrations of biomolecules that affect the structure and stability of RNA/DNA hybrid duplexes. However, the detailed environmental effects remain unclear. Therefore, the mechanistic details of the effect of such molecular crowding were investigated at the molecular level by using thermodynamic and nuclear magnetic resonance analyses, revealing structure-dependent destabilization of the duplexes under crowded conditions. The transition from B- to A-like hybrid duplexes due to a change in conformation of the DNA strand guided by purine-pyrimidine asymmetry significantly increased the hydration number, which resulted in greater destabilization by the addition of cosolutes. By quantifying the individual contributions of environmental factors and the bulk structure of the duplex, we developed a set of parameters that predict the stability of hybrid duplexes with conformational dissimilarities under diverse crowding conditions. A comparison of the effects of environmental conditions in living cells and in vitro crowded solutions on hybrid duplex formation using the Förster resonance energy transfer technique established the applicability of our parameters to living cells. Moreover, our derived parameters can be used to estimate the efficiency of transcriptional inhibition, genome editing, and silencing techniques in cells. This supports the usefulness of our parameters for the visualization of cellular mechanisms of gene expression and the development of nucleic acid-based therapeutics targeting different cells.

A graphene oxide-based platform for the assay of RNA synthesis by RNA polymerase using a fluorescent peptide nucleic acid probe

We report a simple, direct fluorometric assay based on graphene oxide (GO) for RNA polymerase-mediated RNA synthesis. In principle, fluorescent peptide nucleic acid (PNA) probes were designed, and annealed with RNA products and the resultant RNA-PNA hybrids induced the recovery of fluorescence intensity of the PNA probes adsorbed onto the GO surface.

Structure of a T7 RNA polymerase elongation complex at 2.9 A resolution

The single-subunit bacteriophage T7 RNA polymerase carries out the transcription cycle in an identical manner to that of bacterial and eukaryotic multisubunit enzymes. Here we report the crystal structure of a T7 RNA polymerase elongation complex, which shows that incorporation of an 8-base-pair RNA-DNA hybrid into the active site of the enzyme induces a marked rearrangement of the amino-terminal domain. This rearrangement involves alternative folding of about 130 residues and a marked reorientation (about 130 degrees rotation) of a stable core subdomain, resulting in a structure that provides elements required for stable transcription elongation. A wide opening on the enzyme surface that is probably an RNA exit pathway is formed, and the RNA-DNA hybrid is completely buried in a newly formed, deep protein cavity. Binding of 10 base pairs of downstream DNA is stabilized mostly by long-distance electrostatic interactions. The structure implies plausible mechanisms for the various phases of the transcription cycle, and reveals important structural similarities with the multisubunit RNA polymerases.