Upstream stimulatory factor 1 (USF1), also name Class B basic helix-loop-helix protein. It is a major late transcription factor. USF1 is 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. USF1 has been linked to familial combined hyperlipidemia (FCHL). The USF1 exists two isoform and the calculated molecular weight of USF1 is a 32 kDa and 27 kDa. USF1 has acetylated form and phosphorylated form, so the molecular weight of USF1 can migrate to about 40 kDa.
