Fig. 1. Genomic structure of the ARF-INK4a locus and sequence comparison of ARF proteins. A, schematic representation of the human ARF-INK4a locus. B, sequence comparison of ARF proteins from different species. Human (Hs, Homo sapiens); mouse (Mm, Mus musculus); rat (Rn, Rattus norvegicus); gray opossum (Md, Monodelplus domestica). C, schematic representation of HDM2 protein. Various functional motifs are indicated below and regions for binding with p53 (33 34 35 36) , p300 (37) , ribosomal protein L5 (40) ,5 ARF (29 , 30 , 32 , 45) , and MDMX (92) are indicated above. Vertical line, a cysteine or histidine residue in the zinc or RINF finger.