Regulation der transkriptionellen Aktivität der Isoformen des Drosophila melanogaster Ecdysteroid-Rezeptors (EcR)
FacultiesFakultät für Naturwissenschaften
LicenseStandard (Fassung vom 01.10.2008)
The insect nuclear receptors Ecdysteroid Receptor (EcR) and Ultraspiracle (Usp) are the key regulators of moulting and metamorphosis, mediating the effects of ecdysteroids (moulting hormones) in target cells by modulating the expression of hormone-dependent genes. Regulation of transcriptional activity of the three Drosophila melanogaster EcR isoforms, EcR-A, EcR-B1 and EcR-B2, and their main heterodimerization partner Usp is investigated in this work. Transcriptional activity of the EcR isoforms is not only modulated by regulation of receptor protein stability, intracellular localization and DNA binding of the EcR/Usp complex, but also by intramolecular interaction of the isoform-specific AB-domain of EcR with the ligand binding domain (LBD). As analyzed by FRET technique (fluorescence resonance energy transfer), the N-terminal AB-domain of EcR thereby modulates the position of helix 12 of the LBD in the unliganded receptor as well as repositioning of helix 12 upon hormone binding in an isoform-specific manner. In case of EcR-A, the N-terminal AB-domain additionally functions as an intramolecular repressor of transcriptional activity, resulting in lower transactivation potency of EcR-A compared to EcR-B1 and EcR-B2. Even in the absence of a ligand, helix 12 of Drosophila Usp is known to be locked in an antagonistic position. As demonstrated by point mutations enhancing the flexibility of Usp helix 12, the position of helix 12 influences the receptor stability of EcR, nuclear localization, DNA binding and transcriptional activity of EcR and Usp. Thus, fixation of Usp helix 12 in the unusual antagonistic position is important for the main receptor functions of the Drosophila melanogaster EcR/Usp heterodimer.
Subject HeadingsEcdysteroide [GND]
Nuclear receptors [LCSH]
Fluorescence resonance energy transfer [MeSH]