Stimulates the activity of serine palmitoyltransferase (SPT). Interacts with the serine palmitoyltransferase complex LCB1-LCB2. Component of the SPOTS complex, at least composed of LCB1/2 (LCB1 and/or LCB2), ORM1/2 (ORM1 and/or ORM2), SAC1 and TSC3.