QUANTITATIVE STUDY OF MOTHER-DAUGHTER ASYMMETRY IN Ace2 LOCALIZATION IN YEAST

LUCIA DURRIEU; MUNZER U; ALAN BUSH; GUNNAR CEDERSUND; ALEJANDRO COLMAN LERNER

Puerto Madryn - Chubut

Congreso; 46th Annual Meeting Argentine Society for Biochemistry and Molecular Biology XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

Society for Biochemistry and Molecular Biology XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Saccharomyces cerevisiae reproduces by budding, a process that is intrinsically asymmetric. Mother cells form buds that separate to become daughters. Three asymmetric processes have been studied the most: mating type switching, replicative aging, and Ace2-driven daughter cell-specific gene expression. The molecular mechanism that leads to the activation of the third process is not fully understood. The transcription factor Ace2 is seen in both nuclei at the end of mitosis, but disappears from the mother´s nucleus soon after. Localization of a protein to the nucleus is the net result of import and export reactions. To gain insight into the mechanism responsible for Ace2 asymmetry, we developed a method based on FRAP that enables us to calculate nuclear transport rates from individual live cells. We found that the ratios between the import and export rates are similar in mothers and in their daughters. This result is surprising as equal ratios imply equal nuclear fractions. However, absolute transport rates are asymmetric: mother cells have significantly slower nuclear shuttling dynamics than their daughters. Yeast maintain this kinetic asymmetry actively since we found regulatory mutations that result in inverted behavior. Our results allowed us to reject previous mechanisms for Ace2 asymmetry and propose a new, dynamic, model.reproduces by budding, a process that is intrinsically asymmetric. Mother cells form buds that separate to become daughters. Three asymmetric processes have been studied the most: mating type switching, replicative aging, and Ace2-driven daughter cell-specific gene expression. The molecular mechanism that leads to the activation of the third process is not fully understood. The transcription factor Ace2 is seen in both nuclei at the end of mitosis, but disappears from the mother´s nucleus soon after. Localization of a protein to the nucleus is the net result of import and export reactions. To gain insight into the mechanism responsible for Ace2 asymmetry, we developed a method based on FRAP that enables us to calculate nuclear transport rates from individual live cells. We found that the ratios between the import and export rates are similar in mothers and in their daughters. This result is surprising as equal ratios imply equal nuclear fractions. However, absolute transport rates are asymmetric: mother cells have significantly slower nuclear shuttling dynamics than their daughters. Yeast maintain this kinetic asymmetry actively since we found regulatory mutations that result in inverted behavior. Our results allowed us to reject previous mechanisms for Ace2 asymmetry and propose a new, dynamic, model.