RGT2

Rgt2 is a membrane-bound glucose sensor protein in the budding yeast Saccharomyces cerevisiae. It belongs to the Rgt2/Snf3 family of glucose sensors and is predicted to be a multi-pass transmembrane protein located in the plasma membrane. While related in sequence to hexose transporters, Rgt2 functions primarily as a sensor rather than a transporter.

In the glucose signaling pathway, Rgt2 works together with its paralog Snf3 to detect extracellular glucose and regulate the expression of hexose transporter genes (HXT). When glucose is detected, the signal is transmitted through a regulatory cascade that involves the transcription factor Rgt1 and the corepressors Mth1 and Std1. Under glucose-rich conditions, Mth1 and Std1 are targeted for ubiquitin-mediated degradation by the SCF-Grr1 ubiquitin ligase complex, relieving repression at HXT promoters and promoting the appropriate transcription of hexose transporters.

A key functional distinction between the two sensors is their glucose affinity. Snf3 is generally considered the high-affinity sensor for low external glucose, whereas Rgt2 serves as a low-affinity sensor that responds to higher glucose concentrations. Together, they enable the cell to adjust hexose transporter expression across a range of sugar availabilities.

Genetically, deletion of RGT2 alone partially impairs high-glucose signaling, with Snf3 providing some compensatory signal. In contrast, combined loss of RGT2 and SNF3 abolishes the extracellular glucose sensing pathway, illustrating the redundancy and cooperative function of these sensors in regulating HXT gene expression.

Rgt2 is of interest for studies on metabolic regulation and sugar sensing in yeast, and its activity informs broader understanding of how cells adapt transporter expression to nutrient availability.