ARF peptide, is the alternative frame (ARF) tumour suppressor protein which is expressed on the occurrence of oncogenic stimuli. It functions to prevent abnormal cell proliferation through inhibiting the p53 ubiquitin ligase protein Mdm2 from degrading p53. This results in the increased stability of the p53 tumour suppressor causing G1 cell cycle arrest. Additionally mouse ARF proteins can localise E2F1 and c-Myc transcriptions factors to the nucleolus therefore they are no longer able to activate S-phase promoting target gene. Again this results in cell cycle arrest, ultimately preventing tumour cell growth. It is evident that if the expression of the ARF peptide is inhibited tumour formation is more likely to occur.