Regulator of the DNA damage response (DDR). Part of the TTT complex that is required to stabilize protein levels of the phosphatidylinositol 3-kinase-related protein kinase (PIKK) family proteins. Promotes assembly, stabilizes and maintains the activity of TORC complexes, which regulate cell growth and survival in response to nutrient and hormonal signals. May be involved in telomere length regulation (By similarity). Belongs to the TEL2 family. Extended N-terminus.