Regulatory subunit of the trehalose synthase complex that catalyzes the production of trehalose from glucose-6-phosphate and UDP-glucose in a two step process. May stabilize the trehalose synthase complex, and confer sensitivity to physiological concentrations of phosphate and to fructose 6-phosphate. The trehalose synthase complex is composed of the two catalytic subunits TPS1 and TPS2, and at least one of the two regulatory subunits TPS3 or TSL1. Repressed by glucose. C-terminal 700 AA are mainly in alpha-helices and beta-sheets. Present with 1960 molecules/cell in log phase SD medium. In the C-terminal section; belongs to the glycosyltransferase 20 family.