The ability to regulate transgene expression levels is essential for many functional genomic and therapeutic applications. In an Advanced Online Publication in Nature Biotechnology, Wilfried Weber and colleagues describe the development of E.REX, a novel gene regulation system that exploits components of the Escherichia coli erythromycin-resistance regulon (Nat Biotechnol 2002, DOI:10.1038/nbt731).

They designed both E_OFF and E_ON systems that are respectively repressed or induced using macrolide antibiotics (including erythromycin, clarithromycin and roxithromycin). Weber et al. demonstrated that the E.REX systems can function in mammalian cell lines in culture and in microencapsulated cells transplanted into mice. The binary E.REX system is functionally compatible with the tetracyline-responsive system allowing for the design of simultaneously regulated multigene applications.