Receptor for ecdysone (PubMed:1913820, PubMed:30293839). Binds to ecdysone response elements (ECRES) following ecdysone-binding, and recruitment of a complex containing the histone methyltransferase trr, leads to activate transcription of target genes (PubMed:1913820, PubMed:30293839). Heterodimer of USP and ECR (PubMed:8247157). Only the heterodimer is capable of high-affinity binding to ecdysone (PubMed:8247157). Interacts with trr in an ecdysone-dependent manner (PubMed:14603321). Upon ecdysone stimulation, interacts with Nup98 (PubMed:28366641). Isoform B1 predominates over isoform A in larval tissues, imaginal histoblast nests and midgut islands. Isoform A predominates over B1 in imaginal disks, and the larval prothoracic gland. In the salivary glands of mid instar larvae levels increase during puff stage 1 at 86-94 hours of development then remain relatively constant until the premetamorphic pulse of ecdysone in late larvae. Levels diminish dramatically from puff stage 7 onwards. Levels increase in the prepupal period during puff stage 13-14, the level remains stable until stage 21. A decrease in levels at puff stage 7 is also seen in the Malpighian tubules and less dramatically in the fat body and gut. In the wing disk the relatively low level remains unchanged. RNAi-mediated knockdown blocks ecdysone-dependent fat body cell migration into the pupal head. Belongs to the nuclear hormone receptor family. NR1 subfamily. Truncated N-terminus.