Dai, W., Zhang, G. and Makeyev, E.V.
Notes: The full-length 3´ UTR of mouse RNA-binding protein HuR was amplified and cloned into psiCHECK™-1 Vector to create pEM429 plasmid. To generate radiolabeled RNA substrates for use in cleavage assays, RNA was synthesized from 1µg of linearized plasmid using 50µCi of [α-32P]UTP, 0.8mM Ribo m7G Cap Analog and T7 RNA Polymerase by incubating for 1.5 hours at 37°C. The RNAs were then treated with 1 unit of RQ1 RNase-Free DNase per 1µg of template DNA for 15 minutes at 37°C before extracting with phenol:chloroform, precipitating with ethanol and resuspending in DEPC-treated water. The cleavage assay used 60fmol of 32P-labeled substrate RNA with 10U Recombinant RNAsin Ribonuclease Inhibitor in a reaction incubated for 2.5 hours at 30°C. RNA probes were labeled with biotin using T7 or T3 RNA Polymerases with a biotin-UTP labeling NTP mixture and incubated for 2 hours at 37°C. The biotinylation reaction was then treated with RQ1 RNase-Free DNase following the same protocol used for radiolabeled RNA. To form HuR/RNA complexes, 2µg of biotinylated RNA was mixed with 100µg nuclear extract and 40 units Recombinant RNAsin® Ribonuclease Inhibitor in a total volume of 20µl, and incubated for 30 minutes at room temperature. For CstF-64/RNA complexes, 1µg of biotinylated RNA was used and the complexes were stabilized by UV crosslinking using 10U Recombinant RNAsin Ribonuclease Inhibitor during the UV treatment. NIH 3T3 cells were UV crosslinked and either total or nuclear RNA used for immunoprecipitation. After extraction the RNAs were treated with RQ1 RNase-Free DNase for 15 minutes at 37°C before RT-PCR using HuR-specific primers. Total RNA purified from cultured cells were incubated with 50U/ml RQ1 RNase-Free DNase at 37°C for 30 minutes before use in RT-qPCR. (4187)