Abstract: A regulatable gene expression construct comprising a nucleic acid molecule comprising a two-way riboswitch operably linked to a target sequence. Also provided is a library screening strategy for efficient creation of target-specific riboswitches. A theophylline-repressible and IPTG-inducible riboswitch device achieves portable control of gene expression control in a ‘two-way’ manner. The default state of target genes is ON; the targets are switched off by adding theophylline, and switched back to the ON-state by adding IPTG without changing growth medium. The riboswitch device regulates gene expression in a portable, adjustable, and two-way manner with a variety of scientific and biotechnological applications.