The research in our lab focuses on elucidating basic mechanisms of localized translation in eukaryotes, with emphasis on translation near the ER and mitochondria. We apply various methods, including electron microscopy, biochemical purification, molecular biology, in vivo fluorescent imaging and functional genomics to understand how mRNAs approach the ER and mitochondria, what are the RNA sequences that regulate this localization and which proteins are involves.
Localized translation near the Mitochondria
Mitochondria proteins were considered for many years to be translated in the cytosol, and to be imported to the mitochondria only when fully translated. In recent years, however, an alternative model was revived, in which proteins are translated near the mitochondria and thus may be imported more efficiently. This model is based on studies of mRNA localization, that showed that many different mRNAs that encode mitochondrial proteins are in close proximity to the outer membrane of the mitochondria.We have shown that a protein receptor of the outer
membrane (Tom20) affects mRNA localization to the mitochondria (Eliyahu E. et al 2010) and that cytosolic chaperones are also involved in this process (Eliyahu et al 2012). Most recently we identified a novel receptor (OM14) for cytosolic ribosomes on yeast mitochondria outer membrane. In vitro, this receptor is important for co-translational import of proteins, and thus provide a strong support to the idea that localized translation near the mitochondria improves that efficiency of protein import (Lesnik et al 2014). Currently we are searching for partners of this receptor, and whether its role is conserved in mammalian cells.
mRNA localization to the ER
Many mRNAs are known to associated with the ER, and locally synthesize membrane or secreted proteins into this organelle. The most studied mechanism for targeting these mRNAs to the ER involves association of the SRP with the n
ascent protein chain, as it emerges from the ribosome. However, work in the last few years, including from our lab (Loya A. et al 2008) revealed that mRNAs can be localized also in a manner that does not necessitate translation. We found the 3’UTR sequences are important for ER-association and we are now searching for the proteins that mediate this translation independent localization. One candidate is the Puf2 protein, that was shown to interact with ER-destined mRNAs. We found that Puf2 has a unique binding motif ( a dual UAAU sequence)(Yosefzon Y. et al 2011) and a role in response to high calcium (Haramati O. et al 2017). The The role of Puf2 in ER targeting, as well as the importance of the UAAU motif are now under investigation in my lab.