The mammalian CDKN2A locus contains a gene that encodes two unrelated proteins: the cyclin-dependent kinase inhibitor p16INK4a and ARF, a regulator of p53 stability. In the Early Edition of the Proceedings of the National Academy of Sciences Kim et al. report that the chicken genome lacks an INK4a orthologue and has a truncated ARF gene (Proc Natl Acad Sci USA 2002, 10.1073/pnas.0135557100). Sequencing of genomic and cDNA clones revealed the structure around the chicken CDKN2A locus. The chicken genome lacks the INK4a-specific primary exon1α. Furthermore, splicing of the chicken ARF transcript generates a stop codon and a truncated 60-residue protein. This truncated chicken ARF protein was localized to the nucleolus and increased p53 stability in human cells.