|M.Sc Student||Ben-Haim Oded|
|Subject||A New Role for Transcription Factor in mRNA Degradation|
|Department||Department of Medicine||Supervisor||PROF. Mordechai Choder|
|Full Thesis text|
Messenger RNAs (mRNAs) levels in the cell are controlled by two major mechanisms: transcription and decay. Nevertheless, the cross talk between the two mechanisms is relatively unknown. Several years ago, it was found in our group that the yeast RNA polymerase II subunits Rpb4 and Rpb7 play roles both in mRNA transcription and degradation. We assume that cross talk between transcription and the mRNA decay pathways is crucial for the appropriate control of gene expression. Our group has found that Rpb4p interacts with Sfp1p, a transcription factor that controls the synthesis of mRNAs encoding Ribosome Proteins (RP). We revealed that Sfp1p is involved in mRNA degradation; this role is dependent on its capacity to interact with Rpb4p. Furthermore, I found that Sfp1p and Rpb4p co-sediments with polyribosomes, thus raising the possibility that Sfp1p may have a role in translation. In addition to Sfp1p, there are other RP transcription factors responsible for the transcription of RP genes, among them are Ifh1p, Crf1p, Fhl1p and Rap1p. Sfp1p and Ifh1p are considered to function as activators, Crf1p as repressor; Fhl1p functions as the scaffold of the complex which binds directly to the DNA and Rap1p recruits Fhl1p. In order to examine if Ifh1p, Crf1p, Fhl1p and Rap1p have a role in mRNA degradation we tested these factors in a degradation assay. The experiments where done at non permissive temperature, in which transcription was arrested, so the decay rate was the major process that influenced the mRNA levels. I found that Fhl1p has a stabilizing effect on PBF mRNA but plays no role in the decay of non-PBF mRNAs, while Ifh1, Crf1 and Rap1 did not have a noticeable effect on degradation. We have found that Fhl1p and Sfp1p are required for efficient mRNA stabilization and this function of both of them depends on Rpb4. Like Rpb4p; Fhl1p and Sfp1p are specifically involved in both synthesis and decay of mRNAs encoding Protein Biosynthetic Factors (PBF). We propose that Fhl1p recruits Sfp1 to PBF promoters, while Sfp1p and Rpb4/7 are shuttling in complex with mRNA. In the cytoplasm they mediate the decay of PBF mRNA and at least Rpb4/7 has a role in translation. In this way Sfp1p and Rpb4/7 couple between transcription in the nucleus and mRNA decay in the cytoplasm.