ETS1 and ETS2, activated by RAS/RAF/MAP kinase cascade, bind the promoter of p16INK4A in the CDKN2A locus (Ohtani et al. 2001). CDKN2A locus also encodes p14ARF (p19ARF in mouse), but from a different promoter and in a different reading frame. While p16INK4A and p14ARF use different exon 1, (exon 1-alpha and exon 1-beta, respectively), they share exons 2 and 3. However, because the reading frames are different, there is no amino acid sequence similarity between the two proteins (Quelle et al. 1995).