RECENT ADVANCES IN INDUCIBLE GENE-EXPRESSION SYSTEMS

A means of controlling the level and timing of expression of specific genes in cultured cells or in animals would have broad applications. T here has been recent progress in two very promising systems: problems due to the high background expression from tetracycline-responsive pro moters have been solved by constructing tetracycline-sensitive transcr iptional repressors; and new rapamycin analogues have been isolated th at are capable of activating the FK506-inducible system but lack the c ytostatic side effects of the original inducers. Both systems now prov ide opportunities for expressing toxic genes, growth arrest genes, and therapeutic products in a regulated fashion previously not possible.