FIGURE 24-26 The INK4b-ARF-INK4a locus encodes three tumor-suppressor genes. Exons are designated as E. The two INK4b exons (orange) are located upstream of the ARF/INK4a locus. ARF (blue) is encoded by a unique E1β exon but shares exons E2 and E3 with INK4a (green). INK4b and INK4a encode p15 and p16, respectively. ARF encodes a p53 activator.

[Data from C. Sherr, 2006, Nat. Rev. Cancer 6:663–673.]