How do yeast cells sense glucose?

A glucose-sensing mechanism has been described in Saccharomyces cerevisiae that regulates expression of glucose transporter genes. The sensor proteins Snf3 and Rgt2 are homologous to the transporters they regulate. Snf3 and Rgt2 are integral plasma membrane proteins with unique carboxy-terminal domains that are predicted to be localized in the cytoplasm. In a recent paper Ozcan and colleagues [Ozcan S, et al. EMBO J 1998; 17:2556-2773 (Ref. 1)] present evidence that the cytoplasmic domains of Snf3 and Rgt2 are required to transmit a glucose signal. They provide additional evidence to support their earlier assertion [Ozcan S, et al. Proc Natl Acad Sci USA 1996;93:12428-12432 (Ref. 2)] that glucose transport via Snf3 and Rgt2 is not involved in glucose sensing but, rather, that these proteins behave like glucose receptors. Other examples of transporter homologs with regulatory functions have recently been described in fungi as well [Madi L, et al. Genetics 1997; 146:499-508 (Ref. 3). and Didion T, et al. Mol Microbiol 1998;27:643-650 (Ref. 4)]. The identification of this class of nutrient sensors is an important step in elucidating the complex of regulatory mechanisms that leads to adaptation of fungi to different environments.