Positive selection of DNA-protein interactions in mammalian cells through phenotypic coupling with retrovirus production

Through the shuffling of predefined modular zinc finger (ZF) domains with predictable target site recognition in vitro, we have generated a large repertoire of artificial transcription factors (ATFs) with five ZF domains (TF(ZF)s). Here we report an effective strategy for the selection of ATF libraries through the coupling of the expression of transcriptional activators of the promoter of interest to the enhanced production of retroviral vector particles transferring the gene encoding the TF(ZF.) Using this strategy, we successfully selected specific TF(ZF)s that upregulate the expression of the γ-globin promoter. Selected transcription factors induced the expression of γ-globin when coupled to an activation domain and reduced expression when linked to a repression domain. This novel retroviral approach might be used to select other TF(ZF)s but also might be generalized for the selection of other protein and small molecule interactions.