Identification and regulation of a gene required for cell fusion during mating of the XXXX @entity375 .

@entity6771 @entity5679 @entity6770 @entity5678 @entity40723 @entity9457 @entity375
We have devised a screen for genes from the @entity375 @entity375 whose expression is affected by cell type or by the mating pheromones. From this screen we identified a gene, @entity40723 , whose pattern of expression revealed interesting regulatory strategies and whose product was required for efficient cell fusion during mating. Transcription of @entity40723 occurred only in a and alpha cells, not in a/alpha cells, where it was repressed by a1 X alpha 2, a regulatory activity present uniquely in a/alpha cells. Transcription of @entity40723 showed an absolute requirement for the products of five STE genes, @entity5679 , @entity5678 , @entity6771 , @entity6770 , and @entity9457 . Since the activators @entity5679 , @entity5678 , and @entity9457 are themselves repressed by a1 X alpha 2, the failure to express @entity40723 in a/alpha cells is probably the result of a cascade of regulatory activities; repression of the activators by a1 X alpha 2 in turn precludes transcription of @entity40723 . In addition to regulation of @entity40723 by cell type, transcription from the locus increased 10-fold or more when a or alpha cells were exposed to the opposing mating pheromone. To investigate the function of the @entity40723 protein, we created @entity40723 null mutants. In @entity40723 X @entity40723 matings, the cells of a mating pair adhered tightly and appeared to form zygotes. However, the zygotes were abnormal. Within the conjugation bridge the contained a partition that prevented nuclear fusion and mixing of organelles. The predicted sequence of the @entity40723 protein (deduced from the @entity40723 DNA sequence) and subcellular fractionation studies with @entity40723 -beta-galactosidase hybrid proteins suggest that @entity40723 is a membrane or secreted protein. Thus, @entity40723 may be located at a position within the cell where it is poised to catalyze cell wall or plasma membrane fusion.
