Pescadillo was originally identified in the zebrafish Danio rerio as a site of a retrovirus-insertion mutation that caused severe defects during embryogenesis. In particular, growth of the fetal zebrafish liver was significantly affected by loss of pescadillo function. To begin to understand the role of pescadillo during mammalian hepatogenesis we identified the murine homologue of pescadillo and named it Pes1. A single gene localized to chromosome 11 on the mouse genome encodes Pes1. Although Pes1 mRNA was detected in all tissues examined it was present at the highest levels in both adult and fetal liver. Analysis of the predicted amino acid sequence of Pes1 found it to contain a BRCT domain, which has previously been found in several proteins involved in cell-cycle checkpoints and DNA repair. Consistent with a putative role in these processes we found that when recombinant Pes1 protein was expressed in HepG2 cells it localized to the nucleus.