Genetics of nonsense suppressors in yeast
<p>This thesis is a genetic study of the cytoplasmically- inherited determinant [psi] of Saccharomyces cerevisiae . [psi] is a potentiator of ochre suppression. The molecular basis of [psi] was investigated using mutagenesis as a probe. The <em>psi</em><sup>+</sup> phe...
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| Format: | Thesis |
| Language: | English |
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1978
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| _version_ | 1797071484852633600 |
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| author | Tuite, M |
| author2 | Cox, B |
| author_facet | Cox, B Tuite, M |
| author_sort | Tuite, M |
| collection | OXFORD |
| description | <p>This thesis is a genetic study of the cytoplasmically- inherited determinant [psi] of Saccharomyces cerevisiae . [psi] is a potentiator of ochre suppression. The molecular basis of [psi] was investigated using mutagenesis as a probe. The <em>psi</em><sup>+</sup> phenotype (efficient suppression) can be mutated to <em>psi</em><sup>-</sup> phenotype (loss of suppression) by ultra-violet light (UV) and nitrosoguanidine (NTG) . The UV-induced mutation was a single-hit event and the pre-mutational lesion was partly photoreactivable . Repair or expression of UV-induced mutation to the [psi] determinant was under the same genetic control as for nuclear mutation. It was concluded that [psi] has a DNA genome. The 'extrachromosomal mutagens' thymidylate starvation, 5-fluorouracil, manganese chloride and cycloheximide failed to induce <em>psi</em><sup>-</sup> mutants whilst guanidine hydrochloride, dimethyl sulphoxide and potassium chloride were shown to induce this mutation at frequencies up to 100%. Several other physical and chemical agents caused a high frequency of loss of the <em>psi</em><sup>+</sup> phenotype.</p> <p>A new class of recessive nuclear mutation (<em>pnm</em>) was shown to cause a loss of the <em>psi</em><sup>+</sup> phenotype. A simple comple- mentation test was devised to distinguish them from cytoplasmic <em>psi</em><sup>-</sup> mutants. The dominant PNM<sup>-</sup> mutation was shown not to cause a physical loss of the [psi] genome. Two mutants with a modified PNM<sup>-</sup> phenotype were analysed. Attempts to demon- strate genetically the involvement of [psi] with the 80S ribosome were unsuccessful. The <em>psi</em><sup>+</sup> phenotype was conclusively demonstrated to be inherited independently' of the nucleus using a 'heterokaryon test'. Two models for the [psi] phenomena were proposed; one postulating the presence of a DMA 'plasmid' and one postulating the involvement of a stable, self-perpetuating metabolic state.</p> |
| first_indexed | 2024-03-06T22:53:56Z |
| format | Thesis |
| id | oxford-uuid:5fbf8bef-22ce-4471-8d4e-b37f285343c1 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T22:53:56Z |
| publishDate | 1978 |
| record_format | dspace |
| spelling | oxford-uuid:5fbf8bef-22ce-4471-8d4e-b37f285343c12022-03-26T17:48:50ZGenetics of nonsense suppressors in yeastThesishttp://purl.org/coar/resource_type/c_db06uuid:5fbf8bef-22ce-4471-8d4e-b37f285343c1GeneticsYeastSaccharomyces cerevisiaeEnglishPolonsky Theses Digitisation Project1978Tuite, MCox, BCox, B<p>This thesis is a genetic study of the cytoplasmically- inherited determinant [psi] of Saccharomyces cerevisiae . [psi] is a potentiator of ochre suppression. The molecular basis of [psi] was investigated using mutagenesis as a probe. The <em>psi</em><sup>+</sup> phenotype (efficient suppression) can be mutated to <em>psi</em><sup>-</sup> phenotype (loss of suppression) by ultra-violet light (UV) and nitrosoguanidine (NTG) . The UV-induced mutation was a single-hit event and the pre-mutational lesion was partly photoreactivable . Repair or expression of UV-induced mutation to the [psi] determinant was under the same genetic control as for nuclear mutation. It was concluded that [psi] has a DNA genome. The 'extrachromosomal mutagens' thymidylate starvation, 5-fluorouracil, manganese chloride and cycloheximide failed to induce <em>psi</em><sup>-</sup> mutants whilst guanidine hydrochloride, dimethyl sulphoxide and potassium chloride were shown to induce this mutation at frequencies up to 100%. Several other physical and chemical agents caused a high frequency of loss of the <em>psi</em><sup>+</sup> phenotype.</p> <p>A new class of recessive nuclear mutation (<em>pnm</em>) was shown to cause a loss of the <em>psi</em><sup>+</sup> phenotype. A simple comple- mentation test was devised to distinguish them from cytoplasmic <em>psi</em><sup>-</sup> mutants. The dominant PNM<sup>-</sup> mutation was shown not to cause a physical loss of the [psi] genome. Two mutants with a modified PNM<sup>-</sup> phenotype were analysed. Attempts to demon- strate genetically the involvement of [psi] with the 80S ribosome were unsuccessful. The <em>psi</em><sup>+</sup> phenotype was conclusively demonstrated to be inherited independently' of the nucleus using a 'heterokaryon test'. Two models for the [psi] phenomena were proposed; one postulating the presence of a DMA 'plasmid' and one postulating the involvement of a stable, self-perpetuating metabolic state.</p> |
| spellingShingle | Genetics Yeast Saccharomyces cerevisiae Tuite, M Genetics of nonsense suppressors in yeast |
| title | Genetics of nonsense suppressors in yeast |
| title_full | Genetics of nonsense suppressors in yeast |
| title_fullStr | Genetics of nonsense suppressors in yeast |
| title_full_unstemmed | Genetics of nonsense suppressors in yeast |
| title_short | Genetics of nonsense suppressors in yeast |
| title_sort | genetics of nonsense suppressors in yeast |
| topic | Genetics Yeast Saccharomyces cerevisiae |
| work_keys_str_mv | AT tuitem geneticsofnonsensesuppressorsinyeast |