The lipid phosphatase Sac1p inhibits transport out of the Golgi and, based on its expected target, should increase transport out of the ER. Now, Faulhammer et al. find that Sac1p switches from its ER role to the Golgi role in response to lower nutrient levels, thus reducing trafficking and providing an initial link between growth and secretion (page 185).
Faulhammer et al. found that Sac1p localized to the ER during exponential growth and was retained there by a direct interaction with an integral ER membrane protein called dolichol phosphate mannose synthase, or Dpm1p. When the researchers transferred these fast growing cells to nutrient-poor media, Sac1p moved to the Golgi within minutes.