Bud10p directs axial cell polarization in budding yeast and resembles a transmembrane receptor.
BACKGROUND
The budding yeast Saccharomyces cerevisiae can bud in two spatially programmed patterns: axial or bipolar. In the axial budding pattern, cells polarize and divide adjacent to the previous site of cell separation, in response to a cell-division remnant, which includes Bud3p, Bud4p and septin proteins. This paper investigates the role of an additional component of the cell-division remnant, Bud10p, in axial budding.


RESULTS
The sequence of Bud10p predicts a protein that contains a single trans-membrane domain but lacks similarity to known proteins. Subcellular fractionations confirm that Bud10p is associated with membranes. Bud10p accumulates as a patch at the bud site prior to bud formation, and then persists at the mother-bud neck as the bud grows. Towards the end of the cell cycle, the localization of Bud10p refines to a tight double ring which splits at cytokinesis into two single rings, one in each progeny cell. Each single ring remains until a new concentration of Bud10p forms at the developing axial bud site, immediately adjacent to the old ring. Certain aspects of Bud10p localization are dependent upon BUD3, suggesting a close functional interaction between Bud10p and Bud3p.


CONCLUSIONS
Bud10p is the first example of a transmembrane protein that controls cell polarization during budding. Because Bud10p contains a large extracellular domain, it is possible that Bud10p functions in a manner analogous to an extracellular matrix receptor. Clusters of Bud10p at the mother-bud neck formed in response to Bud3p (and possibly to an extracellular cue, such as a component of the cell wall), might facilitate the docking of downstream components that direct polarization of the cytoskeleton.
Halme
A
A
Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, Massachusetts 02138, USA.
Michelitch
M
M
Mitchell
E L
EL
Chant
J
J
D000595:Amino Acid Sequence; D001483:Base Sequence; D016764:Cell Polarity / Q000502:physiology*; D017931:DNA Primers; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000166:cytology*; D029701:Saccharomyces cerevisiae Proteins
C104374:BUD10 protein, S cerevisiae; D017931:DNA Primers; D005656:Fungal Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins