Study of an amino acid transporter that lost its transport activity and evolved into a sensor of external amino acids

Ssy1 is a protein similar in sequence to yeast amino-acid permeases but is devoid of transport activity. Its role is rather to detect the presence of external amino acids and to activate a signalling pathway that leads to transcriptional induction of several genes encoding amino acid permeases, e.g.. AGP1 encoding a broad-specificity permease. The genetic dissection of the pathway activated by Ssy1 led to the important finding that ubiquitin (Ub) and an SCF-type Ub-ligase complex play an essential role in this pathway.

We currently try to better understand the exact role of Ub and this SCF Ub ligase in transcriptional induction of Ssy1-regulated genes. Furthermore, as Ssy1 most likely derived during evolution from a classical amino acid permease, we also aim to understand the structural features conferring to Ssy1 its signalling properties.