The fau gene is the cellular homolog of the fox sequence in the Finkel-Biskis-Reilly Murine Sarcoma Virus (FBR-MuSV). This virus acquired the fau sequence in its reversed transcriptional orientation. Human and mouse fau cDNA's were identified and both encode a new protein of 133 AA. We show that fau (for FBR-MuSV associated ubiquitiously expressed gene) becomes expressed in all different tissues tested as a 600 bp messenger and we report the genomic structure of the human fau gene. The gene consists of five exons and four introns and the 5' untranslated region displays characteristic features for a housekeeping gene. Fau encodes the ribosomal protein S30 fused to a Ubiquitin-like protein.