Upstream Transcription Factor 1 (USF1)

USF1 encodes a member of the basic helix-loop-helix leucine zipper family, and can function as a cellular transcription factor. The encoded protein can activate transcription through pyrimidine-rich initiator (Inr) elements and E-box motifs. This gene has been linked to familial combined hyperlipidemia (FCHL). Two transcript variants encoding distinct isoforms have been identified for this gene. USF1 can act synergistically with GTF2I  to activate transcription through both pyrimidine-rich initiator (Inr) elements and E-box elements of the adenovirus major late promoter. By mutation analysis, they determined that this synergistic action requires both the activation and dimerization domains of USF1. By in vitro cotranslation followed by coimmunoprecipitation studies, they confirmed direct protein interaction between GTF2I and USF1.