Ste50

Ste50 is an adaptor protein in the budding yeast Saccharomyces cerevisiae, encoded by the STE50 gene. It functions within the pheromone response pathway, acting to relay signals from activated pheromone receptors toward the pheromone-activated mitogen-activated protein kinase (MAPK) cascade. Ste50 associates with the MAPKKK Ste11 and other signaling components, helping to assemble or stabilize the signaling complex and thereby modulate the strength and fidelity of the response to mating pheromones.

Through its interactions, Ste50 contributes to pheromone-induced transcription and mating efficiency. Genetic studies show that loss of STE50 reduces transcription of pheromone-responsive genes and impairs mating under certain conditions, indicating that Ste50 enhances or refines signal transmission rather than serving as a core catalytic component of the cascade. Some evidence also points to roles for Ste50 in other signaling contexts, consistent with crosstalk among MAPK pathways in yeast.

Structurally, Ste50 is a cytoplasmic protein that contains interaction domains enabling binding to Ste11 and other partners. The Ste50-Ste11 interaction is part of a conserved signaling module in fungi, and STE50 homologs are found in many fungal species, suggesting a broadly conserved adaptor function in MAPK signaling beyond Saccharomyces cerevisiae.

Overall, Ste50 serves as a conditionally important adaptor that shapes pheromone signaling, contributing to the regulation and specificity of the yeast MAPK pathway during mating and related responses. It is not essential for viability but is routinely studied to understand how adaptor proteins influence MAPK cascade architecture in fungal systems.