The Role of fnx1, a Fission Yeast Multidrug Resistance Protein, in the Transition of Cells to a Quiescent G₀ State

ABSTRACT

Most microorganisms live in conditions of nutrient limitation in their natural habitats. When exposed to these conditions they respond with physiological and morphological changes that enable them to survive. To obtain insights into the molecular mechanisms of this response a systematic genetic screen was performed to identify genes that when overexpressed can induce a starvation-like response in the yeast species Schizosaccharomyces pombe. One gene that meets these criteria, fnx1⁺, induces, transcriptionally correlates with, and is required for the entry into the quiescent G₀ state that is normally induced by nitrogen starvation. fnx1⁺ encodes a protein with sequence similarity to the proton-driven plasma membrane transporters from the multidrug resistance group of the major facilitator superfamily of proteins. We propose that fnx1⁺plays a role in the entry into G₀, possibly by facilitating the release of a signaling substance into the environment as a means of cell-to-cell communication.

ACKNOWLEDGMENTS

This work was supported by grant MCB-9513714 from the National Science Foundation.

We thank Adam Kuspa, Richard Atkinson, Sandra S. Salus, and Janos Demeter for their valuable comments and suggestions and Maureen McLeod, Susan Forsburg, and Tony Carr for providing us with S. pombe strains and vectors.