Introduction of multiple genes into cells and translation and expression of them are increasingly required for engineering and understanding biological systems. Small-molecule-responsive translational regulatory systems are widely known and have been used for expressing transgenes. Such a method is a technique to equally regulate expression of multiple genes.
Up to the present, quantitative regulation of the expression of a protein from an exogenous gene in a eukaryote largely depends on a transcription factor responsive to added small molecules such as tetracycline (Deans T L, Cantor C R, Collins J J (2007) A tunable genetic switch based on RNAi and repressor proteins for regulating gene expression in mammalian cells. Cell 130:363-372). The activity of the transcription factor is determined depending upon the concentration of added effector molecules. Such a combination of effector molecules and a transcription factor equally regulates transcription levels of multiple target genes in a cell. FIG. 16 is a conceptual diagram of such a conventional system.
Post-transcriptional regulation of a target gene in a mammalian cell has been also reported (Okano H et al. (2005) Function of RNA-binding protein Musashi-1 in stem cells. Exp Cell Res. 306: 349-356).
The present inventors designed a target mRNA containing a kink-turn RNA motif, that is, a binding RNA motif of an archaeal ribosomal protein, L7Ae protein, and reported a “translation OFF switch” system for strongly decreasing the translation of this mRNA (WO2009/066757). FIG. 15 illustrates the structure of the kink-turn RNA motif and a brief outline of the system. The system functions as an On-Off switch. However, the use is restricted for quantitative translational regulation.