mRNA targeting to the endoplasmic reticulum in budding yeast

01/12/2015 to 30/11/2018

The endoplasmic reticulum (ER) is the entry point for most proteins destined for secretion or those of the cell’s endomembrane system. In the classical model of ER targeting, proteins are delivered to the ER in a signal recognition particle- (SRP-) and translation-dependent manner. However, recent observations suggest the existence of alternative or supplementary pathways, including translation-independent targeting of mRNAs to the ER and their local translation at its surface. Translation-independent mRNA targeting or membrane-tethered translation has been detected in cells ranging from yeast to humans and several biological functions for such a mechanism have been proposed. Localization of mRNAs to the ER can for example contribute to control the protein composition of ER subdomains by sorting proteins before their translocation and thus provide a more subtle control over an organelle’s protein configuration. Targeting of mRNAs to ER can be mediated by RNA-binding proteins (RBPs) that are either ER membrane proteins or dynamically associate with ER. In a coordinated approach with three other groups of the FOR2333 we plan to identify biologically relevant RBPs that mediate mRNA targeting to ER and other organelles in mammals and fungi, identify their target mRNAs by database search or experimental approaches including crosslinking combined with immunoprecipitation (CLIP) or crosslinking combined with rapid amplification of cDNAs (CRAC), and determine the biological role of RBP-controlled mRNA targeting for cell function. In addition, we will elucidate the binding mechanism to ER for two membrane-associating RBPs, yeast She2p and Khd1p, applying a novel proximity labeling technique, BioID to identify their interaction partners. This approach will enable us to analyze mechanistic aspects of RBP-membrane interaction, including how soluble RBPs recognize specific organelle membranes and which membrane or membrane-associated proteins participate in the recognition. Results from the proposed will expand our view on intracellular sorting mechanisms and might lead to new and evolutionary conserved concepts for cellular sorting logistics controlled by RNA-binding proteins.