Nuclear receptor cofactor for the ecdysone-regulated processes of molting and puparium formation. Acts downstream from ecdysone biosynthesis and release to control the expression of specific ecdysone-regulated genes such as Eip74EF (E74). Interacts with nuclear receptors EcR, svp (seven up), usp (ultraspiracle), Hr39 and Hr3. During second and third instar larval development, it is localized primarily to the cytoplasm of cells in the brain and imaginal disks (tissues that are fated to form specific parts of the adult fly during metamorphosis). Also localized to the cytoplasm of larval salivary gland cells during the second and early third instar stages. It however, begins to shift into the nucleus of these cells in the mid-third instar maintaining this localization through the end of larval development. At puparium formation, it shuttles out of the nucleus of salivary gland cells to become more abundant in the cytoplasm. A similar dynamic movement occurs in cells of the larval midgut during third instar development. Component of U bodies. Expressed in the brain and salivary glands of early and late second instar larvae. Expressed in nurse cells and oocytes. Contains one Leu-Xaa-Xaa-Leu-Leu (LXXLL) motif, which is usually essential for the association with nuclear receptors.