Thesis (M.Sc.)--York University, 2003. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 122-134). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ86279

The Tetrahymena thermophila rDNA minichromosome has been used as a model system for studying DNA replication. Previous studies have identified cis-acting replication determinants within the rDNA origin and promoter region including the type I element that is essential for replication initiation, fork progression and promoter activation. TIF1 is a non-ORC single strand-binding protein that binds the type I element in vivo. TIF1 binds opposing strands at the origin and promoter regions indicating that it may play a role in selectively marking these regions. In this dissertation, I use gene disruption to elucidate the role of TIF1 in replication. This work reveals that TIF1 represses rDNA origin firing, and is required for proper macronuclear S phase progression and division. Replication at the rDNA origin initiates precociously despite the observation that TIF1 mutants exhibit an elongated macronuclear S phase and a diminished rate of DNA replication. The amitotic macronucleus also displays delayed and abnormal division even though cells exit S phase with a wild-type macronuclear DNA content. Nuclear defects are also evident in the diploid micronucleus as TIF1 mutants contain fewer micronuclear chromosomes and are unable to pass genetic information to progeny. This defect is progressive as clonal mutant lines exhibit micronuclear instability during subsequent vegetative cell cycling. This work reveals that these macro- and micronuclear phenotypes may be the result of DNA damage as TIF1 mutants are hypersensitive to DNA damaging agents. This suggests that TIF1 mutants may have defects in the DNA damage response pathway. TIF1-deficient cells also incur DNA damage with no exogenous damaging agents. I propose that micro- and macronuclear defects witnessed in TIF1 mutant cells result from cells exiting S phase with compromised chromosomes due to the accumulation of DNA damage. Furthermore, TIF1 appears to play a role in the prevention, recognition or repair of DNA damage in addition to regulating rDNA replication and cell cycle progression and division. Additionally, TIF1 plays an essential role in the faithful propagation of both the macro- and micronuclear genomes.

Thesis (M. Phil.)--University of Hong Kong, 1986.

published_or_final_version / Biochemistry / Master / Master of Philosophy

The nucleotide sequence of cnjB, a conjugation specific gene of Tetrahymena thermophila, has been determined. The gene encodes a putative polypeptide (CnjB) of 1748 amino acids with a calculated molecular weight of 200 kilodaltons and a pI of 7.9. Four transcription start sites were mapped. The gene has only one genomic copy and is not conserved in yeast (as determined by cross-hybridization experiments with yeast DNA). Analysis of the 13 introns in cnjB, accompanied by 15 other T. thermophila intron sequences, shows that they resemble the nuclear pre-mRNA introns of other eukaryotes. / The carboxy-terminal third of CnjB has three regions with repetitive sequences. One region contains seven retroviral-type zinc fingers and the others contain repeated glycine-rich motifs, a motif seen in the heterogeneous nuclear ribonuclear proteins A1 and A2/B1. Proteins with these motifs have single-strand binding and strand annealing activity. / Synthetic phosphorothioate oligonucleotides antisense to regions of the isoleucyl tRNA synthetase gene transcript did not affect cell growth in a sequence-specific manner when cultures of T. thermophila were grown in their presence.

The nucleotide sequence of the cnjA cDNA (formerly pC1) from the ciliated protozoan Tetrahymena thermophila was determined. This gene was previously found to be conjugation specific and to peak in expression just prior to or at pachytene in meiotic prophase I. The cnjA message is initiated from four transcription start sites, one minor and three major, and encodes a putative protein (CnjA) of 779 amino acids. The protein has a calculated molecular weight of 89.5 kDa and is mainly hydrophilic with an estimated pI of 9.3. CnjA was found to share no sequence similarities with any known protein to date. The gene's coding region demonstrates an unusual codon choice. Flanking regions of the cnjA genomic locus were amplified by means of the Inverse PCR method but attempts at subcloning and characterizing its promoter region were unsuccessful.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, December 2000. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1974. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 254-271).

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.