Ash1, a Daughter Cell-Specific Protein, Is Required for Pseudohyphal Growth of Saccharomyces cerevisiae

ABSTRACT

Ash1 (for asymmetric synthesis of HO) was first uncovered in genetic screens that revealed its role in mating-type switching. Ash1 prevents HO expression in daughter cells. Because Ash1 has a zinc finger-like domain related to that of the GATA family of transcription factors, it presumably acts by repressingHO transcription. Nonswitching diploid cells also express Ash1, suggesting it could have functions in addition to regulation ofHO expression. We show here that Ash1 has an essential function for pseudohyphal growth. Our epistasis analyses are consistent with the deduction that Ash1 acts separately from the mitogen-activated protein kinase cascade and Ste12. Similarly to the case in yeast form cells, Ash1 is asymmetrically localized to the nuclei of daughter cells during pseudohyphal growth. This asymmetric localization reveals that there is a previously unsuspected daughter cell-specific function necessary for pseudohyphal growth.

ACKNOWLEDGMENTS

This research was supported by Public Health grant GM-39852 from the National Institutes of Health.

We thank H. Liu and G. Fink for providing yeast strains and pIL30 and pCG37 plasmids, A. Sil and I. Herskowitz for providing pAS163, J. Pringle for providing pKS+GFP, M. Ward and S. Garrett for providing pMW2, and S. Ramer and S. Elledge for providing the pYES-R yeast genomic DNA expression library. We are also grateful to E. D. Salmon and E. Yeh for use of the microscope facility and for sharing their expertise with us and to R. Duronio, J. Heitman, and S. Kron for critical reading of the manuscript and helpful discussions.