Sangpen Chamnongpol

Co-translational mRNA decay in Saccharomyces cerevisiae

The rates of RNA decay and transcription determine the steady-state levels of all messenger RNA and both can be subject to regulation. Although the details of transcriptional regulation are becoming increasingly understood, the mechanism(s) controlling mRNA decay remain unclear. In yeast, a major pathway of mRNA decay begins with deadenylation followed by decapping and 5′–3′ exonuclease digestion. Importantly, it is hypothesized that ribosomes must be removed from mRNA before transcripts are destroyed. Contrary to this prediction, here we show that decay takes place while mRNAs are associated with actively translating ribosomes. The data indicate that dissociation of ribosomes from mRNA is not a prerequisite for decay and we suggest that the 5′–3′ polarity of mRNA degradation has evolved to ensure that the last translocating ribosome can complete translation.

Direct detection of small RNAs using splinted ligation

This protocol describes a method for direct labeling and detection of small RNAs present in total RNA by splinted ligation. The assay uses a small RNA-specific bridge oligonucleotide to form base pairs with the small RNA and a 5′-end-radiolabeled ligation oligonucleotide. The captured small RNA is directly labeled by ligation. Detection of the labeled small RNAs is performed by denaturing gel electrophoresis and autoradiography or phosphorimaging. This protocol has been successfully used to study expression of various classes of biological small RNAs from nanogram to microgram amounts of total RNA without an amplification step. It is significantly simpler to perform and more sensitive than either northern blotting or ribonuclease protection assays. Once the oligonucleotides have been synthesized and total RNA has been extracted, the procedure can be completed in 6 h.

Cotranslational microRNA mediated messenger RNA destabilization

MicroRNAs are small (22 nucleotide) regulatory molecules that play important roles in a wide variety of biological processes. These RNAs, which bind to targeted mRNAs via limited base pairing interactions, act to reduce protein production from those mRNAs. Considerable evidence indicates that miRNAs destabilize targeted mRNAs by recruiting enzymes that function in normal mRNA decay and mRNA degradation is widely thought to occur when mRNAs are in a ribosome free state. Nevertheless, when examined, miRNA targeted mRNAs are invariably found to be polysome associated; observations that appear to be at face value incompatible with a simple decay model. Here, we provide evidence that turnover of miRNA-targeted mRNAs occurs while they are being translated. Cotranslational mRNA degradation is initiated by decapping and proceeds 5’ to 3’ behind the last translating ribosome. These results provide an explanation for a long standing mystery in the miRNA field. DOI: http://dx.doi.org/10.7554/eLife.12880.001

SH3 domain protein-binding arrays.

First identified as part of the Rous sarcoma oncogene product Src, SH3 (Src Homology 3) domains play an important role in intercellular communication and intracellular signal transduction. A high-throughput assay for ligand binding to SH3 domains--SH3 domain proteins immobilized on a membrane--allows rapid visualization of numerous SH3 domain protein-protein interactions with no expensive equipment or radioactivity required. Once the array is constructed or obtained commercially, the procedure is straightforward: The protein of interest is cloned into a fusion-tagged expression vector and expressed in bacteria, the prepared bacterial extract is incubated with the array membrane, and the signal is measured using a chemiluminescence detection system.

Abstract 1797: Differential gene expression profiles of FFPE samples with SensationPlus™ and GeneChip™ arrays.

Formalin-fixed and paraffin-embedded (FFPE) tissue samples represent a largely untapped wealth of information on the transcriptional states of clinically archived materials for retrospective studies. Although the RNA is degraded during fixation and storage and has been considered unusable, Affymetrix has developed SensationPlus™, a target-preparation method that allows transcriptional profiling from 20 ng of FFPE total RNA using GeneChip™ arrays. We will demonstrate that SensationPlus™ expression profiles from decade old FFPE materials are extremely similar to data from their matched fresh frozen (FF) RNA counterparts. Citation Format: Sangpen Chamnongpol, Andrea Ujvari, Olga Kourennaia, Kim Myers, Lisa Bowers, Jesse Fisher, Marc Post, Chris Kubu. Differential gene expression profiles of FFPE samples with SensationPlus™ and GeneChip™ arrays. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1797. doi:10.1158/1538-7445.AM2013-1797