Complete sequencing of the murine USF gene and comparison of its genomic organization to that of mFIP/USF2.

USF is a transcription factor able to stimulate promoter activity upon binding to an upstream sequence identical to that recognized by the protooncogene Myc. However, despite extensive biochemical characterization, nothing is known concerning its physiological function. A USF-related protein able to interact with Fos and known as FIP/USF2 has been reported. Its genomic structure in mouse has been recently characterized. We present here the cloning and characterization of the murine USF gene. It consists of 10 exons, the first of which is noncoding, and the gene spans 8 kb of DNA. We show that the murine USF protein is almost identical to its human counterpart, but that an intron not conserved between human and murine USF genes curiously has been conserved between human USF and murine FIP/USF2. Otherwise, the splicing pattern of murine USF and FIP/USF2 is exactly conserved. We also demonstrate that the murine USF promoter is located more than 2.5 kb upstream of the first coding ATG, in a region displaying divergent promoter activity. Finally, we show that an Mx1-related sequence is present less than 3 kb downstream of the murine USF gene, in a tail-to-tail position. Taken together, these data indicate that the murine USF gene is very similar to the murine FIP/USF2 gene and is potentially bracketed by two other transcription units on the other DNA strand.