TRIzol solubilization and extraction is a relatively recently developed general method for deproteinizing RNA. This method is particularly advantageous in situations where cells or tissues are enriched for endogenous RNases or when separation of cytoplasmic RNA from nuclear RNA is impractical. TRIzol (or TRI Reagent) is a monophasic solution of phenol and guanidinium isothiocyanate that simultaneously solubilizes biological material and denatures protein. After solubilization, the addition of chloroform causes phase separation (much like extraction with phenol:chloroform:isoamyl alcohol), where protein is extracted to the organic phase, DNA resolves at the interface, and RNA remains in the aqueous phase. Therefore, RNA, DNA, and protein can be purified from a single sample (hence, the name TRIzol). TRIzol extraction is also an effective method for isolating small RNAs, such as microRNAs, piwi-associated RNAs, or endogeneous, small interfering RNAs. However, TRIzol is expensive and RNA pellets can be difficult to resuspend. Thus, the use of TRIzol is not recommend when regular phenol extraction is practical.

Purification of RNA using TRIzol (TRI reagent).

Glial Lipid Droplets and ROS Induced by Mitochondrial Defects Promote Neurodegeneration

Rewiring of the Fruit Metabolome in Tomato Breeding.

MicroRNAs (miRNAs) act within Argonaute proteins to guide repression of messenger RNA targets. Although various approaches have provided insight into target recognition, the sparsity of miRNA-target affinity measurements has limited understanding and prediction of targeting efficacy. Here, we adapted RNA bind-n-seq to enable measurement of relative binding affinities between Argonaute-miRNA complexes and all sequences ≤12 nucleotides in length. This approach revealed noncanonical target sites specific to each miRNA, miRNA-specific differences in canonical target-site affinities, and a 100-fold impact of dinucleotides flanking each site. These data enabled construction of a biochemical model of miRNA-mediated repression, which was extended to all miRNA sequences using a convolutional neural network. This model substantially improved prediction of cellular repression, thereby providing a biochemical basis for quantitatively integrating miRNAs into gene-regulatory networks.

https://science.sciencemag.org/content/sci/early/2019/12/04/science.aav1741.full.pdf

The biochemical basis of microRNA targeting efficacy

Sequence, Structure, and Context Preferences of Human RNA Binding Proteins

One of the oldest and simplest (and still very useful) methods for detecting RNA-protein interactions is the filter-binding assay. If a mixture of RNA and protein is passed through a nitrocellulose filter, the protein will be retained and the RNA will pass through. But if the protein is capable of binding RNA, then RNA will be retained on the filter as well. This protocol requires a purified protein (or chromatographic fractions) of interest and (32)P-labeled RNA. To perform the assay, the protein sample is serially diluted to several concentrations. It is then mixed with a fixed amount of radioactive RNA and allowed to bind under desired conditions for 30-60 min. The binding reactions are then applied to a 96-well dot-blot apparatus with low vacuum to trap the complexes on three membranes: The top membrane traps aggregates, the middle membrane (nitrocellulose) binds proteins and RNA-protein complexes, and the bottom membrane (which is charged) collects free RNA. After washing and drying, the membranes are exposed to phosphor-imaging screens for quantitation. Alternatively, single, larger filters (that can be counted in a scintillation counter) and a filter manifold can be used.

Filter-binding assay for analysis of RNA-protein interactions.

This protocol describes a method for RNA purification by sodium dodecyl sulfate (SDS) solubilization and phenol extraction. It is of wide utility and is used routinely to deproteinize RNAs in biological material that has been solubilized in SDS, an ionic detergent that dissolves membranes, disrupts protein-nucleic acid interactions, and inactivates ribonucleases. Once solubilized, addition of phenol or phenol:chloroform:isoamyl alcohol (PCA) completely denatures the protein, and it becomes insoluble in aqueous solution. PCA extraction is the method of choice for preparing cytoplasmic RNA from tissue culture cells or in any other situation (e.g., enzyme reactions) where solubilization in SDS is easily achievable.

Purification of RNA by SDS Solubilization and Phenol Extraction

It often is desirable to "prefractionate" RNA before analysis. Ordinarily, this can only be done with tissue culture cells, although it is possible to isolate nuclei and cytoplasm from certain "soft" tissues such as liver and white blood cells. This protocol describes a method for separating nuclei from the cytoplasm that can be used for many tissue culture types. This procedure also is useful for cells grown in suspension or for adherent cells. The procedure relies on swelling in hypotonic buffer, subsequent gentle homogenization, and centrifugation. This method is not appropriate for material (e.g., bacteria, yeast) that has high intrinsic RNase activity, or tissues that are difficult to solubilize, such as muscle tissue or plant material.

Preparation of Cytoplasmic and Nuclear RNA from Tissue Culture Cells

This protocol describes the detection of small RNAs (10–200 nucleotides) by blot hybridization. The RNA samples, denatured in formamide, are separated by denaturing polyacrylamide gel electrophoresis. Becausehigh-percentage polyacrylamide gels arerequired toseparateRNAs in this sizerange, it is necessary to perform electrophoretic transfer to positively charged nylon membranes. After transfer, the immobilized RNAs are subjected to hybridization with a 32 P-radiolabeled DNA or RNA probe and detected by phosphorimaging or autoradiography. This procedure is commonly used to detect small, U-rich spliceosomal small nuclear RNAs (snRNAs) and miRNAs. It should be possible also to detect most miRNAs using high-percentage (e.g., 15%) urea–polyacrylamide gel electrophoresis.

/pdf/northern-blots-for-small-rnas-and-micrornas-35h269t8hf.pdf

Donald C. Rio

Papers

Purification of RNA using TRIzol (TRI reagent).

Filter-binding assay for analysis of RNA-protein interactions.

Purification of RNA by SDS Solubilization and Phenol Extraction

Preparation of Cytoplasmic and Nuclear RNA from Tissue Culture Cells

Northern blots for small RNAs and microRNAs.