Recombinant Drosophila melanogaster E3 ubiquitin-protein ligase Topors (Topors), partial

Functions as a ubiquitin-protein E3 ligase. Negatively regulates the transcriptional repressor h/hairy by promoting its ubiquitination and subsequent degradation. Also directs the nuclear organization of the gypsy chromatin insulator. Chromatin insulators are regulatory elements which establish independent domains of transcriptional activity within eukaryotic genomes. Insulators have two defining properties; they can block the communication between an enhancer and a promoter when placed between them, and can also buffer transgenes from position effect variegation (PEV). Insulators are proposed to structure the chromatin fiber into independent domains of differing transcriptional potential by promoting the formation of distinct chromatin loops. This chromatin looping may require the formation of insulator bodies, where homotypic interactions between individual subunits of the insulator complex could promote the clustering of widely spaced insulators at the nuclear periphery. Within the gypsy insulator complex, this protein may promote formation of nuclear insulator bodies by recruiting individual insulator complexes to the nuclear lamina.