Figure 1.

Photolabile protection groups and their application in this work. A) A variety of previously published photolabile protection groups with improved aqueous solubility or membrane permeability based on the NB photocaging group. B) Three photolabile protection groups were used in this work to construct the photocaged IPTG variants NP‐cIPTG (1), BEC‐cIPTG (10 a) and BC‐cIPTG (10 b), strongly differing in their water solubility. These caged inducer molecules (red dot with blue frame) are biologically inactive; however, upon illumination with UV‐A light, their activity can be restored by a two‐step cleavage process. Subsequently, the IPTG binds the repressor protein LacI releasing LacI from the P_T7, P_tac or P_grac promoter and thus inducing gene expression. This principle was applied to analyse the effect of cIPTG solubility on the inducibility of LacI repressor‐controlled target gene expression in E. coli, P. putida, and B. subtilis.