|M.Sc Student||Cohen Shlomit|
|Subject||Effects of Single-Stranded DNA Binding Proteins on the|
Activity of the Enzyme Telomerase
|Department||Department of Biology||Supervisors||Professor Gadi Schuster|
|Professor Haim Manor|
In this thesis, I present a biochemical analysis of the effects of three single-stranded DNA binding proteins on extension of oligonucleotide primers by the Tetrahymena telomerase. One of them, a human protein designated translin, which was shown to selectively bind the G-rich Tetrahymena and human telomeric repeats, was found to slightly stimulate the primer extension reactions at molar ratios of translin/primer of <1/2. At higher molar ratios, it inhibited the reactions by up to 80%. The inhibition was caused by binding of translin to the primers, rather than by a direct interaction of this protein with telomerase. A second protein, the general human single-stranded DNA binding protein RPA, similarly affected the primer extension by telomerase, even though its mode of binding to DNA differed from that of translin. A third protein, the E. coli SSB, whose binding to DNA is highly cooperative, caused more substantial stimulation and inhibition at the lower and the higher molar ratios of SSB/primer, respectively. Both telomere-specific and general single-stranded DNA binding proteins are found in living cells in telomeric complexes. Farther more, translin and RPA were able to inhibit the human telomerase in vitro. Based on these data, I propose that these proteins may exert either stimulatory or inhibitory effects on telomerase in the cells, depending on their local concentrations that may vary under different physiological conditions.