guanosine-triphosphate and 2--3--dideoxythymidine-triphosphate

Telomerase, which synthesizes telomeric DNA in eukaryotic cells, is classified as a reverse transcriptase. To clarify the susceptibility of telomerase to nucleoside 5'-triphosphates bearing a hydrophobic group on the base moiety, we studied the inhibitory effects of 2',3'-dideoxy-5-styryluridine 5'-triphosphate analogues and 9-(beta-D-arabinofuranosyl)-2-(p-n-butylanilino)purine 5'-triphosphate analogues on telomerase activity using a quantitative 'stretch PCR' assay. 2',3'-Dideoxy-5-styryluridine 5'-triphosphate (StddUTP) showed more potent inhibition than 2',3'-dideoxythymidine 5'-triphosphate (ddTTP). On the other hand, 9-(beta-D-arabinofuranosyl)-2-(p-n-butylphenyl)guanine 5'-triphosphate (BuParaGTP) showed no inhibition, even though 9-(beta-D-arabinofuranosyl)guanine 5'-triphosphate (araGTP) is a potent inhibitor of telomerase. The influence on telomerase of hydrophobic substituents on the base moieties of nucleotides is described.

Topics: Arabinonucleotides; Dideoxynucleotides; Enzyme Inhibitors; Guanosine Triphosphate; Humans; In Vitro Techniques; Kinetics; Nucleosides; Structure-Activity Relationship; Telomerase; Thymine Nucleotides; Uridine Triphosphate

The ribonucleoprotein enzyme telomerase is a specialized type of cellular reverse transcriptase which synthesizes one strand of telomeric DNA, using as the template a sequence in the RNA moiety of telomerase. We analyzed the effects of various nucleoside analogs, known to be chain-terminating inhibitors of retroviral reverse transcriptases, on Tetrahymena thermophila telomerase activity in vitro. We also analyzed the effects of such analogs on telomere length and maintenance in vivo, and on vegetative growth and mating of Tetrahymena cells. Arabinofuranyl-guanosine triphosphate (Ara-GTP) and ddGTP both efficiently inhibited telomerase activity in vitro, while azidothymidine triphosphate (AZT-TP), dideoxyinosine triphosphate (ddITP) or ddTTP were less efficient inhibitors. All of these nucleoside triphosphate analogs, however, produced analog-specific alterations of the normal banding patterns seen upon gel electrophoresis of the synthesis products of telomerase, suggesting that their chain terminating and/or competitive actions differ at different positions along the RNA template. The analogs AZT, 3'-deoxy-2',3'-didehydrothymidine (d4T) and Ara-G in nucleoside form caused consistent and rapid telomere shortening in vegetatively growing Tetrahymena. In contrast, ddG or ddI had no effect on telomere length or cell growth rates. AZT caused growth rates and viability to decrease in a fraction of cells, while Ara-G had no such effects even after several weeks in culture. Neither AZT, Ara-G, acycloguanosine (Acyclo-G), ddG nor ddI had any detectable effect on cell mating, as assayed by quantitation of the efficiency of formation of progeny from mated cells. However, AZT decreased the efficiency of programmed de novo telomere addition during macronuclear development in mating cells.

Topics: Animals; Arabinonucleotides; Base Sequence; Cell Survival; Deoxyguanine Nucleotides; Dideoxynucleotides; DNA Nucleotidylexotransferase; Guanosine Triphosphate; Molecular Sequence Data; Nucleotides; Telomere; Tetrahymena thermophila; Thymine Nucleotides; Zidovudine