SNAP-tag and HaloTag fused proteins for HaSX8-inducible control over synthetic biological functions in engineered mammalian cells

Drug-inducible systems allow biological processes to be regulated through the administration of exogenous chemical inducers. Such methods can be used to study native biological activities, or to control synthetically engineered ones, with temporal and dose-dependent control. However, the number of existing drug-inducible systems is limited, and there remains a need for synthetic biology components that can be combined with the existing toolset and regulated with independent and orthogonal control. Here, we describe new cell engineering components that can be regulated via a heterodimerization of SNAP-tag and HaloTag domains using a selective small molecule crosslinker termed “HaXS8.” The construction and validation of multiple HaXS8-sensitive components are described, including systems for regulating transcription, Cre recombinase activity, and caspase-9 activity in mammalian cells. The systems elaborate the ability to control gene expression, DNA recombination, and apoptosis in cell engineered systems. ### Competing Interest Statement The authors have declared no competing interest.