|M.Sc Student||Selitrennik Michael|
|Subject||A Role for Transcription Factors in mRNA Decay|
|Department||Department of Medicine||Supervisor||Professor Mordechai Choder|
|Full Thesis text|
Controlling appropriate levels of messenger RNAs (mRNAs) is vital for any living cell. mRNA synthesis in the nucleus by RNA polymerase II (Pol II) and mRNA decay by cytoplasmic machineries equally determine these levels. Yet, little is known about possible cross talk between the two compartments.
Pol II is composed of a ten subunit core and a dissociable heterodimer, Rpb4/7.
As part of this research we have found that Rpb4 and Rpb7 are each required for efficient mRNA degradation. Whereas Rpb4 is specifically involved in decay of mRNAs encoding Protein Biosynthetic Factors (PBF), Rpb7 has more general roles in mRNA decay, affecting the decay of both PBF and non-PBF mRNAs, thus raising the possibility that Rpb4p and Rpb7p link between the nuclear and cytoplasmic processes. Here we show that both Rpb4p and Rpb7p shuttle between the nucleus and the cytoplasm. Shuttling kinetics of the two proteins are similar as long as their interaction is possible, suggesting that they shuttle as a heterodimer. Under normal conditions, shuttling of Rpb4p and Rpb7p depends on ongoing transcription. However, during severe stresses of heat shock, ethanol, and starvation, the two proteins shuttle via a transcription-independent pathway. Thus, Rpb4p and Rpb7p shuttle via two pathways, depending on environmental conditions. In addition we have found that Rpb4p interacts with Sfp1p, a transcription factor of PBF genes.
We assume that cross talk between transcription and the major mRNA decay pathways is crucial for the appropriate control of gene expression. Since, Rpb4/7 is a nucleo-cytoplasmic shuttling heterodimer that interacts with Pol II and is required for mRNA decay, we examined whether Sfp1p is also involved in mRNA decay. Here we show that Sfp1p is a shuttling protein, involved in PBF mRNA decay and that its role in mRNA degradation depends on presence of Rpb4p. We propose that Sfp1p and Rpb4/7p are shuttling in complex with mRNA, thus coupling between transcription in the nucleus and mRNA decay in the cytoplasm.