The mammalian CDKN2A locus contains a gene encoding two unrelated proteins; the cyclin-dependent kinase inhibitor p16^INK4a and ARF — a regulator of p53 stability. In the Early Edition of the Proceedings of the National Academy of Sciences, Soo-Hyun Kim and colleagues report that the chicken genome lacks an INK4a orthologue and has a truncated ARF gene (PNAS, 10.1073/pnas.0135557100, December 27, 2002).

Kim et al. sequenced genomic and cDNA clones and 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.