Snf3

Snf3 is a transmembrane protein in Saccharomyces cerevisiae that functions as a glucose sensor rather than a transporter. It forms part of a dual-sensor system with Rgt2 to detect extracellular glucose levels and regulate the expression of hexose transporters, thereby shaping the cell’s capacity to take up glucose.

Structurally, Snf3 is predicted to be a multi-pass membrane protein belonging to the major facilitator superfamily, typically containing multiple transmembrane helices. It features a large cytoplasmic tail at the C-terminus, which is important for signaling. Unlike conventional transporters, Snf3 lacks efficient substrate transport activity due to alterations in residues critical for transport, and its primary role is signaling rather than moving glucose across the membrane.

Functionally, Snf3 and its partner Rgt2 sense extracellular glucose and relay information to the nucleus to regulate hexose transporter gene expression. The signal modulates the activity of the transcription factor Rgt1 and its corepressors Mth1 and Std1, leading to derepression and increased transcription of HXT genes when glucose is available. In glucose-poor conditions, Rgt1 represses these transporters, limiting glucose uptake. This regulatory circuit allows the yeast to adapt transporter expression to ambient glucose concentrations.

Genetically, SNF3 is one of two glucose-sensing genes in yeast, the other being RGT2. Snf3 provides high-affinity glucose detection, complementing Rgt2’s role in low-affinity sensing, and together they coordinate the cellular response to fluctuating glucose in the environment.

See also: Saccharomyces cerevisiae, glucose sensing, HXT transporters, Rgt1, Mth1, Std1.