Title | Kar5p is required for multiple functions in both inner and outer nuclear envelope fusion in Saccharomyces cerevisiae. |
Publication Type | Journal Article |
Year of Publication | 2014 |
Authors | Rogers, JV, Rose, MD |
Journal | G3 (Bethesda) |
Volume | 5 |
Issue | 1 |
Pagination | 111-21 |
Date Published | 2014 Dec 02 |
ISSN | 2160-1836 |
Keywords | Membrane Fusion, Membrane Proteins, Nuclear Envelope, Nuclear Proteins, Protein Structure, Tertiary, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins |
Abstract | <p>During mating in the budding yeast Saccharomyces cerevisiae, two haploid nuclei fuse via two sequential membrane fusion steps. SNAREs (i.e., soluble N-ethylmaleimide-sensitive factor attachment protein receptors) and Prm3p mediate outer nuclear membrane fusion, but the inner membrane fusogen remains unknown. Kar5p is a highly conserved transmembrane protein that localizes adjacent to the spindle pole body (SPB), mediates nuclear envelope fusion, and recruits Prm3p adjacent to the SPB. To separate Kar5p's functions, we tested localization, Prm3p recruitment, and nuclear fusion efficiency in various kar5 mutants. All domains and the conserved cysteine residues were essential for nuclear fusion. Several kar5 mutant proteins localized properly but did not mediate Prm3p recruitment; other kar5 mutant proteins localized and recruited Prm3p but were nevertheless defective for nuclear fusion, demonstrating additional functions beyond Prm3p recruitment. We identified one Kar5p domain required for SPB localization, which is dependent on the half-bridge protein Mps3p. Electron microscopy revealed a kar5 mutant that arrests with expanded nuclear envelope bridges, suggesting that Kar5p is required after outer nuclear envelope fusion. Finally, a split-GFP assay demonstrated that Kar5p localizes to both the inner and outer nuclear envelope. These insights suggest a mechanism by which Kar5p mediates inner nuclear membrane fusion. </p> |
DOI | 10.1534/g3.114.015800 |
Alternate Journal | G3 (Bethesda) |
PubMed ID | 25467943 |
PubMed Central ID | PMC4291462 |
Grant List | R01 GM037739 / GM / NIGMS NIH HHS / United States T32 GM007388 / GM / NIGMS NIH HHS / United States GM007388 / GM / NIGMS NIH HHS / United States GM037739 / GM / NIGMS NIH HHS / United States |