טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentEliyahu Erez
SubjectFactors Involved in mRNA Localization to the Mitochondria
DepartmentDepartment of Biology
Supervisor Professor Yoav Arava
Full Thesis textFull thesis text - English Version


Abstract

Most of the mitochondrial proteins are encoded in the nucleus and need to be imported into the mitochondria. Recent studies have shown that many mRNAs encoding for mitochondrial proteins are associated with the mitochondria's membrane. Elements in the 3' UTR of the mRNA, the mitochondrial targeting signal, sequences along the translated open reading frame and RNA binding proteins were found to be involved in mRNAs localization to the mitochondria, yet the molecular basis of their association is not fully resolved.

In this work we aimed to explore the possible involvement of mitochondria protein receptors and cytosolic chaperones in mRNA localization to the mitochondria's membrane of S.cerevisiae.

Tom20 and Tom70 are the main mitochondria protein receptors that mediate the initial recognition and import of all mitochondrial proteins. Herein I show that both proteins mediate localization of mRNA encoding mitochondrial proteins. Microarray analysis indicated that Tom20 is involved in localization of about 80% of the mRNAs that were analyzed. To execute its role in mRNA localization, Tom20 requires an active translation process and a mitochondrial targeting signal (MTS). The positive charge of the MTS was also found to be important for mRNA localization. While directed the mRNAs are found in an active translation state.

Proteins import into organelles is supported by chaperones. We found that the cytosolic chaperones NAC and Ssa1 and mitochondrial matrix chaperone Ssc1 are also involved in mRNA localization. A genome-wide analysis revealed that depletion of Ssa1p; affect the localization of many mRNAs encoding for mitochondrial proteins, in particular those that contain hydrophobic domains. Preliminary results suggest that the role of Ssa1p in mRNA localization is MTS dependent.

PUF proteins are evolutionary conserved RNA binding proteins. Puf3p was found to be localized to the mitochondria's membrane and to be involved in mRNA localization. Our results show that deletion of Tom20p affect the localization of Puf3p to the mitochondria. We also found that many of the mRNAs that their localization is Tom20 dependent also have Puf3 binding sites in their 3' UTR. Moreover, deletion of Puf3 and Tom20 cause growth difficulties on media that necessities high mitochondria activity, implying genetic interaction between them.

 Overall these results propose a possible mechanism for mRNA association with the mitochondria. Further work is necessary to characterize what other factors and mechanisms are involved in this localization and what is the contribution of mRNA localization for proteins import and cellular physiology.