This gene 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. Alternate Names: upstream stimulatory factor 1; transcription factor USF-1; bHLHb11; Upstream