We have isolated the rat, mouse and human genes of a distant member of the TGF-β superfamily, growth/differentiation factor-15/macrophage inhibiting cytokine-1 (GDF-15/MIC-1) by screening of genomic libraries. All three genes are composed of two exons, and contain one single intron that interrupts the coding sequences at identical positions within the prepro-domain of the corresponding proteins. The predicted proteins contain the structural hallmarks of members of the TGF-β superfamily, including the seven conserved carboxy-terminal cysteine residues that form the cystine knot. The orthologous molecules show the lowest sequence conservation of all members of the TGF-β superfamily. RT-PCR reveals an abundant expression of GDF-15/MIC-1 mRNA in numerous embryonic and adult organs and tissues. Promoter analysis of the rat promoter indicates the presence of multiple regulatory elements, including a TATA-like sequence as well as several SP1, AP-1 and AP-2 sites. Deletion analysis suggests that a 350bp region upstream of the start of the open reading frame appears to be the most important for regulation of transcription.