|Ph.D Student||Portnoy Victoria|
|Subject||The Interplay between Polyadenylation and Degradation of|
RNA in the Three Domains of Life
|Department||Department of Biology||Supervisor||Professor Gadi Schuster|
|Full Thesis text|
Polyadenylation is a process common to almost all organisms. In eukaryotes, stable poly(A) tails are added to the 3’ end of most mRNAs, which is important for mRNA stability and translation initiation. In contrast, polyadenylation can stimulate RNA degradation; a phenomenon witnessed in prokaryotes, organelles and recently, for nucleus- encoded RNA as well. In general, this decay process consists of sequential events including endonucleolytic cleavage, the addition of degradation stimulated poly(A) sequence to the proximal cleavage products, and exonucleolytic degradation.
The major discoveries of this work are: 1) Cyanobacteria were characterized as an organism in which only PNPase is active as the poly(A) polymerase. 2) The first described organisms that metabolize RNA with no polyadenylation were revealed (halophilic and some methanogenic archaea and Mycoplasma). 3) The archaeal exosome was discovered to be the poly(A) polymerase in hyperthermophilic archaea, similar to PNPase in bacteria and organelles. 4) The human PNPase was characterized to be an active phosphorolytic enzyme that differs in several phenomena from its bacteria and chloroplast counterparts.
The results of this work brought us to suggest a possible scenario for the evolution of polyadenylation in which the stable poly(A)-tails located at the 3’ end of nucleus and animal mitochondria encoded mRNAs evolved from the unstable tails of the polyadenylation stimulated degradation pathway.