Analysis of the effects of stress activated protein kinases on the ribosomal frameshift rate in EST3 gene

Telomeres are repeated DNA sequences at the end of chromosomes and are required for protection of genome integrity. They cannot be replicated by normal replication mechanisms. Telomere replications are carried out by specialized enzyme complex called "Telomerase". In S. cerevisiae, telomerase complex consists of Est1p, Est2p and Est3p peptides and special template RNA called TLC1. It is well known that various stress factors affects telomere length and telomerase activities. In this study, the effects of various stress inducing conditions on the +1 PRF in EST3 mRNA was investigated. Our results indicate that amino acid starvation that activates Gcn2p kinase, activates PRF rate in EST3 more than 2-fold in Gcn2p dependent manner. It appears that Gcn2 kinase activity is partially dependent on other subunits Gcn1p and Gcn20p in the regulation of EST3 PRF rate in stress inducing conditions. Moreover, results of this study indicate that osmotic stress which is triggered by high salt and exerted through Hog1p kinase also affects PRF rate in EST3. Application of osmotic stress on S. cerevisiae cells lead to 2-fold increase in the PRF rate of EST3, and this activation was completely dependent on the presence of functional Hog1p. In addition, our results indicates that glucose limitation severely restricts PRF rate in EST3. Growth of yeast cells in non-fermentable carbon sources such as glycerol lactate, resulted with 5 to 6-fold decrease in the PRF efficiency in EST3. We found that glucose limitations exerts its effects on EST3 PRF through Snf1p kinase. Results of this thesis research clearly indicated that PRF rate or PRF efficiency in EST3 mRNA is strictly controlled by SAPK's in S. cerevisiae.