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The yeast Ca(2+)-ATPase homologue, PMR1, is required for normal Golgi function and localizes in a novel Golgi-like
Abstract:
PMR1, a Ca(2+)-adenosine triphosphatase (ATPase) homologue in the yeast Saccharomyces cerevisiae localizes to a novel Golgi-like organelle. Consistent with a Golgi localization, the bulk of PMR1 comigrates with Golgi markers in subcellular fractionation experiments, and staining of PMR1 by indirect immunofluorescence reveals a punctate pattern resembling Golgi staining in yeast. However, PMR1 shows only partial colocalization with known Golgi markers, KEX2 and SEC7, in double-label immunofluorescence experiments. The effect of PMR1 on Golgi function is indicated by pleiotropic defects in various Golgi processes in pmr1 mutants, including impaired proteolytic processing of pro-alpha factor and incomplete outer chain glycosylation of invertase. Consistent with the proposed role of PMR1 as a Ca2+ pump, these defects are reversed by the addition of millimolar levels of extracellular Ca2+, suggesting that Ca2+ disposition is essential to normal Golgi function. Absence of PMR1 function partially suppresses the temperature-sensitive growth defects of several sec mutants, and overexpression of PMR1 restricts the growth of others. Some of these interactions are modulated by changes in external Ca2+ concentrations. These results imply a global role for Ca2+ in the proper function of components governing transit and processing through the secretory pathway.
Insights
The yeast PMR1 gene encodes a Ca(2+)-adenosine triphosphatase (ATPase) crucial for Golgi function. Its absence causes defects in protein processing and glycosylation, highlighting calcium
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- PMR1 is a Ca(2+)-adenosine triphosphatase (ATPase) homologue in Saccharomyces cerevisiae.
- PMR1 localizes to a novel Golgi-like organelle.
- Its precise role in Golgi function was previously unclear.
Purpose of the Study:
- To investigate the localization and function of the yeast PMR1 gene product.
- To determine the role of PMR1 in Golgi trafficking and processing.
- To elucidate the impact of calcium on Golgi apparatus function.
Main Methods:
- Subcellular fractionation to assess PMR1 localization with Golgi markers.
- Indirect immunofluorescence and double-label immunofluorescence to visualize PMR1 and Golgi markers (KEX2, SEC7).
- Analysis of Golgi-related processes (proteolytic processing, glycosylation) in pmr1 mutants.
- Genetic interaction studies with sec mutants under varying calcium concentrations.
Main Results:
- PMR1 localizes to a Golgi-like organelle, partially colocalizing with KEX2 and SEC7.
- pmr1 mutants exhibit defects in pro-alpha factor processing and invertase glycosylation.
- These defects are rescued by millimolar extracellular calcium, indicating calcium's essential role.
- PMR1 function affects secretory pathway transit and processing, with genetic interactions modulated by calcium.
Conclusions:
- PMR1 functions as a Ca(2+) pump essential for normal Golgi apparatus function in yeast.
- Calcium homeostasis is critical for multiple processes within the secretory pathway.
- PMR1 plays a significant role in maintaining the integrity and function of the Golgi complex.