RIP: RNA Immunoprecipitation.

The relevance of RNA-protein interactions in modulating mRNA and noncoding RNA function is increasingly appreciated and several methods have been recently developed to map them. The RNA immunoprecipitation (RIP) is a powerful method to study the physical association between individual proteins and RNA molecules in vivo. The basic principles of RIP are very similar to those of chromatin immunoprecipitation (ChIP), a largely used tool in the epigenetic field, but with some important caveats. The approach is based on the use of a specific antibody raised against the protein of interest to pull down the RNA-binding protein (RBP) and target-RNA complexes. Any RNA that is associated with this protein complex will also be isolated and can be further analyzed by polymerase chain reaction-based methods, hybridization, or sequencing.Several variants of this technique exist and can be divided into two main classes: native and cross-linked RNA immunoprecipitation. The native RIP allows to reveal the identity of RNAs directly bound by the protein and their abundance in the immunoprecipitated sample, while cross-linked RIP leads to precisely map the direct and indirect binding site of the RBP of interest to the RNA molecule.In this chapter both the protocols applied to mammalian cells are described taking into account the caveats and considerations required for designing, performing, and interpreting the results of these experiments.