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Degree

Doctor of Philosophy, Case Western Reserve University, Pathology, 1994.

Abstract

Nucleocytoplasmic transport of macromolecules across nuclear membrane was the essential invention during evolution of eukaryotes. This bidirectional transport is carried out by a machine, the nuclear pore complex, that is anchored in both layers of the nuclear envelope. Although significant progress has been made in understanding of the mechanisms of nuclear protein import, very little is known about the mechanisms of RNA export from nucleus to cytoplasm. To learn molecular and cellular mechanisms of mRNA transport, a genetic approach using Saccharomyces cerevisiae, i.e., the isolation of mRNA transport defective (mtr) mutants followed by their characterization was undertaken. Twenty one temperature sensitive mutants that accumulate polyA⁺RNA in the nucleus at the restrictive temperature were isolated by a suicide selection enrichment procedure and by a screen of random temperature sensitive mutants. These mtr mutants were classified into sixteen different complementation groups, mtr1-mtr16. The mutants also exhibit different accumulation patterns of polyA⁺RNA in the nucleus, suggesting they might have lesions in the different steps of mRNA transport pathway. The first of mtr mutants, mtr1-1 has been characterized in detail and it has multiple defects on RNA processing and transport. Since the structure of mRNA synthesized in mtr1-1 is substantially normal, the mtr1-1 mutation affects the mRNA transport machinery. MTR1 and its homologs are nuclear proteins consisting of seven repeat units and appear to encode guanine nucleotide release proteins on small nuclear GTPases. It is therefore proposed MTR1 and its homologs act as regulators for RNA processing and transport by activating nuclear GTPases. This function is universal in various species and not related to the regulation of cell cycle progression or the state of chromatin organization. The second mtr mutant, mtr2-1 has been characterized, and mRNA export is blocked at the intermediate path of mRNA export in this mutant. PolyA⁺RNA accumulated in the nucleus closely associates with nucleolar proteins, suggesting the possible interaction between the nucleolus and the mRNA transport machinery. MTR2 is a 21kD protein which is poorly expressed and concentrated in the nucleus.

Keywords

Nucleocytoplasmic transport of mRNA Saccharomyces cerevisiae

Advisor

Alan M. Tartakoff

Pages

176p.

Document number: case1057254977
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=case1057254977

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