 INK4a and p14ARF mRNA each consist of three exons.They share exons 2 and 3, but there are two different exon 1 transcripts, α and β. Exon 1β (E1β) is intercalated between the genes for INK4a and INK4b.Although exon 1α (E1α) and E1β are about the same in terms of content and size, the 5’ AUG (start codon) of exon 1β has its own promoter and opens an alternative reading frame in exon 2, hence the name p14ARF (ARF exon 3 is not translated).