Control of cellular function by reversible photoregulation of translation.

The use of light as an external stimulus offers the potential for spatiotemporal control and is thus ideal for controlling gene expression in living cells. In commonly used caging systems, once the caging compound is removed, protein expression cannot be stopped, due to the irreversibility of the uncaging reaction. We have developed a reversible method for regulating protein expression with the aid of a photoresponsive cap that can control the translation of mRNA in a reversible manner through triggering of cis-trans photoisomerization of the cap. In its trans form, the photoresponsive cap completely inhibited translation, whereas the cis form yielded protein (12.7 times more translated protein than in the trans form). Moreover, we succeeded in controlling the levels, timing and duration of protein expression in living mammalian cells. Additionally, neuronal differentiation of PC12 cells was photoinduced by controlling constitutively active H-Ras 61L protein expression.