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Nuclear envelope fusion in the yeast Saccharomyces cerevisiae.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Nuclear envelope fusion in the yeast Saccharomyces cerevisiae./
Author:	Shen, Shu.
Description:	1 online resource (168 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 70-05, Section: B.
Contained By:	Dissertations Abstracts International70-05B.
Subject:	Molecular biology. -
Online resource:	click for full text (PQDT)
ISBN:	9780549771098

Nuclear envelope fusion in the yeast Saccharomyces cerevisiae.
Shen, Shu.

Nuclear envelope fusion in the yeast Saccharomyces cerevisiae. - 1 online resource (168 pages)

Source: Dissertations Abstracts International, Volume: 70-05, Section: B.

Thesis (Ph.D.)--Princeton University, 2008.

Includes bibliographical references

In the yeast Saccharomyces cerevisiae, as in other fungi, the nuclear envelope does not break down during mitosis, meiosis, or conjugation. Nuclear envelope fusion is the final step of the mating pathway, in which two haploid cells mate fuse to become a diploid cell. The nuclear envelope in yeast consists of two phospholipid bilayers, with an embedded spindle pole body. The main topic of this thesis is how two sets of membranes fuse in a coordinated fashion. Several proteins required in nuclear envelope fusion have been found-Prm3p, Kar5p, Kar8p, and Kar2p-but their exact roles are not known. To better understand the mechanism of nuclear envelope fusion, the roles of these proteins are investigated in detail. A recent study in our lab identified Prm3p, a pheromone-induced, peripheral membrane protein found to be required for nuclear membrane fusion (Tobery, 2003). Disruption of PRM3 causes a strong bilateral karyogamy defect, in which nuclear congression has been completed but fusion has not occurred. Electron tomography and time-lapse microscopy show that Prm3p acts at an early step in nuclear envelope fusion. Prm3p is localized around the nuclear envelope, with significant enrichment near the spindle pole body in zygotes. Contrary to a recent study (Beilharz et al., 2003), we demonstrated that Prm3p is resident on the cytoplasmic face of the nuclear envelope. In their study, mutation of a putative NLS in a truncated, non-functional protein led to Prm3p being mislocalized throughout the cytoplasm. Point mutations and deletions of the putative NLS in a fully functional protein had no effect on localization. On the other hand, the highly conserved C-terminus was found to be critical for protein function, localization, and stability. Prm3p's location at the outer nuclear membrane is consistent with its role early in nuclear envelope fusion. Two models have been proposed for nuclear envelope fusion: (1) a one-step model where outer membrane fusion, inner membrane fusion, and spindle pole body fusion occurs simultaneously, and (2) a three-step model where outer membrane fusion is followed by inner membrane fusion and then spindle pole body fusion (Rose, 1996). In collaboration with P. Melloy, electron tomography and time-lapse microscopy were used to demonstrate that nuclear envelope fusion is a three-step process. These techniques were also used to determine the specific roles of proteins required for nuclear envelope fusion. Prm3p acts before or during outer membrane fusion. Kar8p and Kar2p acts during inner membrane fusion. Kar5p appears to have multiple roles, during outer membrane fusion and to couple the outer and inner membranes together. The proteins required for nuclear envelope fusion are likely to act together in one or more fusion complexes. Based on co-immunoprecipitation and affinity pull-down data, Kar5p, Prm3p, and the SNARE proteins Ufe1p and Sec20p appear to interact with each other genetically and physically. They may form a fusogenic complex that acts during outer nuclear membrane fusion. Based on evidence of genetic interactions, Kar2p and Kar8p may form a complex that acts during inner nuclear membrane fusion.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9780549771098Subjects--Topical Terms:

583443
Molecular biology.
Subjects--Index Terms:

Envelope fusionIndex Terms--Genre/Form:

554714
Electronic books.

Nuclear envelope fusion in the yeast Saccharomyces cerevisiae.
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502 $a Thesis (Ph.D.)--Princeton University, 2008.
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520 $a In the yeast Saccharomyces cerevisiae, as in other fungi, the nuclear envelope does not break down during mitosis, meiosis, or conjugation. Nuclear envelope fusion is the final step of the mating pathway, in which two haploid cells mate fuse to become a diploid cell. The nuclear envelope in yeast consists of two phospholipid bilayers, with an embedded spindle pole body. The main topic of this thesis is how two sets of membranes fuse in a coordinated fashion. Several proteins required in nuclear envelope fusion have been found-Prm3p, Kar5p, Kar8p, and Kar2p-but their exact roles are not known. To better understand the mechanism of nuclear envelope fusion, the roles of these proteins are investigated in detail. A recent study in our lab identified Prm3p, a pheromone-induced, peripheral membrane protein found to be required for nuclear membrane fusion (Tobery, 2003). Disruption of PRM3 causes a strong bilateral karyogamy defect, in which nuclear congression has been completed but fusion has not occurred. Electron tomography and time-lapse microscopy show that Prm3p acts at an early step in nuclear envelope fusion. Prm3p is localized around the nuclear envelope, with significant enrichment near the spindle pole body in zygotes. Contrary to a recent study (Beilharz et al., 2003), we demonstrated that Prm3p is resident on the cytoplasmic face of the nuclear envelope. In their study, mutation of a putative NLS in a truncated, non-functional protein led to Prm3p being mislocalized throughout the cytoplasm. Point mutations and deletions of the putative NLS in a fully functional protein had no effect on localization. On the other hand, the highly conserved C-terminus was found to be critical for protein function, localization, and stability. Prm3p's location at the outer nuclear membrane is consistent with its role early in nuclear envelope fusion. Two models have been proposed for nuclear envelope fusion: (1) a one-step model where outer membrane fusion, inner membrane fusion, and spindle pole body fusion occurs simultaneously, and (2) a three-step model where outer membrane fusion is followed by inner membrane fusion and then spindle pole body fusion (Rose, 1996). In collaboration with P. Melloy, electron tomography and time-lapse microscopy were used to demonstrate that nuclear envelope fusion is a three-step process. These techniques were also used to determine the specific roles of proteins required for nuclear envelope fusion. Prm3p acts before or during outer membrane fusion. Kar8p and Kar2p acts during inner membrane fusion. Kar5p appears to have multiple roles, during outer membrane fusion and to couple the outer and inner membranes together. The proteins required for nuclear envelope fusion are likely to act together in one or more fusion complexes. Based on co-immunoprecipitation and affinity pull-down data, Kar5p, Prm3p, and the SNARE proteins Ufe1p and Sec20p appear to interact with each other genetically and physically. They may form a fusogenic complex that acts during outer nuclear membrane fusion. Based on evidence of genetic interactions, Kar2p and Kar8p may form a complex that acts during inner nuclear membrane fusion.
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