The regulation of transcription is the focus of interest. Transcription is the basis for the realization of genetic information, and its regulation is of vital interest for all organisms. Transcriptional regulation is achieved by protein interactions between DNA-bound transcription factors. Split-Ub, an alternative two-hybrid system, is used to analyze these protein interactions inside living cells. Split-Ub is based upon conditional degradation: A protein of interest is fused to the C-terminal half of ubiquitin, which is C-terminally extended by a reporter protein like RUra3p, RGpt2p, or RGFP. In the reporter protein, the fi rst amino acid has been replaced by arginine, an instable residue in the N-end rule pathway of protein degradation.

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