Generation of conditional mutants in higher eukaryotes by switching between the expression of two genes

A regulatory system for the in-depth study of gene functions in higher euka ryotic cells has been developed. It is based on the tetracycline-controlled transactivators and reverse tTA, which mere remodeled to discriminate effi ciently between two different promoters. The system permits one to control reversibly the activity of two genes, or two alleles of a gene, in a mutual ly exclusive way, and also allows one to abrogate the activities of both. T his dual regulatory circuit, which can be operated by a single effector sub stance such as doxycycline, overcomes limitations of conventional genetic a pproaches, The conditional mutants that can now be generated will be useful for the study of gene function in vitro and in vivo. In addition, the syst em may be of value for a variety of practical applications, including gene therapy.