Cajal bodies (coiled bodies, CBs) are nuclear organelles of unknown function and are characterized by a wide variety of components including various basal transcription and cell cycle proteins, the nucleolar proteins fibrillarin and Nopp140, numerous small nuclear ribonucleoproteins, the survival motor neuron protein complex, and the marker protein, p80 coilin. To gain insight into the role of p80 coilin in CBs, we have cloned the murine gene Coil and have mapped it to the distal portion of chromosome band 11D. The similar to 2.6-kb transcript is detectable in all tissues analyzed, with the highest levels in brain and testis. Sequence analysis shows that, like its human counterpart, the mouse coilin gene is composed of seven exons and spans nearly 30 kb of genomic DNA. The predicted amino acid sequence reveals two conserved N- and C-terminal domains, and comparison with the Xenopus SPH-1 protein reveals that these three genes are indeed orthologous. These results should facilitate gene disruption experiments aimed at creating a genetic model system to study CBs.