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Mol. Cell. Biol., 07 1995, 3697-3707, Vol 15, No. 7
J Petersen, D Weilguny, R Egel and O Nielsen
In Schizosaccharomyces pombe, the fus1 mutation blocks conjugation at a
point after cell contact and agglutination. The cell walls separating the
mating partners are not degraded, which prevents cytoplasmic fusion. In
order to investigate the molecular mechanism of conjugation, we cloned the
fus1 gene and found that it is capable of encoding a 1,372-amino-acid
protein with no significant similarities to other known proteins.
Expression of the fus1 gene is regulated by the developmental state of the
cells. Transcription is induced by nitrogen starvation and requires a
pheromone signal in both P and M cell types. Consequently, mutants
defective in the pheromone response pathway fail to induce fus1 expression.
The ste11 gene, which encodes a transcription factor controlling expression
of many genes involved in sexual differentiation, is also required for
transcription of fus1. Furthermore, deletion of two potential Ste11
recognition sites in the fus1 promoter region abolished transcription, and
expression could be restored when we inserted a different Ste11 site from
the mat1-P promoter. Since this element was inverted relative to the fus1
element, we conclude that activation of transcription by Ste11 is
independent of orientation. Although the fus1 mutant has a phenotype very
similar to that of Saccharomyces cerevisiae fus1 mutants, the two proteins
appear to have different roles in the process of cell fusion. Budding yeast
Fus1 is a typical membrane protein and contains an SH3 domain. Fission
yeast Fus1 has no features of a membrane protein, yet it appears to
localize to the projection tip. A characteristic proline-rich potential SH3
binding site may mediate interaction with other proteins.
Copyright © 1995, American Society for Microbiology
Characterization of fus1 of Schizosaccharomyces pombe: a developmentally controlled function needed for conjugation
Department of Genetics, University of Copenhagen, Denmark.
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