|M.Sc Student||Bregman Cohen Almog|
|Subject||A Novel Role for Promoters in mRNA Decay in the Cytoplasm|
|Department||Department of Medicine||Supervisor||PROF. Mordechai Choder|
|Full Thesis text|
Traditionally, the different steps involved in the regulation of gene expression were analyzed separately, leading to the view that they operate independently. More recently, genetic and biochemical analyses have revealed that, rather than being independent, consecutive stages are coupled. Still, relatively little is known about the possible coupling between transcription in the nucleus and mRNA degradation in the cytoplasm. Promoter is defined as the DNA region that directs the transcription initiation by RNA Polymerase II. It is composed of a core element, in the region of the transcription start site, and upstream activating sequence (UAS) that further regulates transcription. In the present study we examined whether the promoter can affect mRNA's decay in the cytoplasm. For this purpose, two different UASs (ACT1 UAS and RPL30 UAS) were hooked upstream of a common transcription unit, which served as a reporter gene. Remarkably, the stability of the reporter mRNAs whose synthesis is controlled by the different UASs was different. Systematic deletion analysis revealed a direct correlation between the presence of two Rap1p-Binding Sites (RapBS) and short half-life. Indeed, insertion of RapBS to ACT1 UAS was sufficient to confer short half-life. Furthermore, deletion of RPL30 RapBS from RPL30 UAS was sufficient to stabilize the transcript. Analyzing the two decay pathways revealed that RapBS affect both 3'-to-5' and 5'-to-3' degradation pathways. This study unveils an additional function for the promoter in the regulation of mRNA decay in the cytoplasm. We propose that the double role of the promoter allows a better coordination between mRNA synthesis and decay to maintain proper levels of mRNAs in the cell. This possible role of promoters in the cytoplasmic mRNA decay pathways represents a new concept in our view of how gene expression is regulated.