Lst1p and Exp1p act in parallel pathways to export the plasma membrane H⁺-ATPase from the ER in S. cerevisiae

Efficient transport of proteins to the correct intracellular compartment is critical for maintaining the functional integrity of the cell. Proteins destined for export from the ER are sorted from ER resident proteins and packaged into vesicles coated with the COPII protein complex. To facilitate our study of the mechanisms of protein sorting, we have selected Pma1p, the plasma membrane H+ ATPase of S. cerevisiae, as a model cargo protein. We found that efficient trafficking of Pma1p to the cell surface requires Lst1p, one of two yeast homologs of the COPII component Sec24p. We initially isolated LSTJ as one of a series of genes whose mutant alleles are lethal in combination with mutant alleles of the COPII gene SEC13. Strains deleted for LSTJ exhibit phenotypes attributable to a defect in Pma1p localization, including sensitivity to growth on acidic medium (pH 3.0) and decreased proton pumping activity. Pma1p accumulates in the ER of Ist1A strains, while other cargo molecules such as invertase and CPY are transported with wildtype kinetics. Like Sec24p, Lst1p specifically binds the COPII component Sec23p. Thus, we propose that Lst1p is an alternative COPII component that selectively exports Pma1p from the ER. We isolated EXP1 (ER-export of Pma1p) as a low-copy suppressor of the lethality displayed by Ist1-] sec13-1 double mutants. Expression of EXP1 from a centromeric plasmid suppresses the sensitivity of IstlA strains to growth on acidic medium and restores plasma membrane localization of Pma1p. Unlike stlA strains, exp1 strains grow normally under acidic conditions.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Kirtley, Michelle Crotwell, 1974-

Advisor dc:contributor.advisor

• Chris A. Kaiser.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/32258

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/32258