The Rat ARF Protein is Translated from Two Closely Spaced ATG Start Codons and Can Transcriptionally Activate p53 in the Absence of p53 Protein Stabilization

We have analyzed the transcriptional start sites of the rat ARF gene and theamino acid sequence of the rat ARF tumor suppressor protein. The 5' end of the ratARF gene is similar to that of a number of cellular housekeeping genes in that it is CGrichand does not contain an upstream TATA box motif to define a precisetranscriptional start site. The transcription of the rat ARF gene is initiated at multiplestart sites with one major start site accounting for 41% of transcription. The rat ARFprotein contains two methionine ATG codons at its amino terminus separated by 10amino acids. The translation of the major endogenous ARF protein species is initiatedfrom the upstream methionine ATG codon. The upstream methionine ATG codon ispredominantly used, despite the fact that it is both very close to the major transcriptionalstart site (6 bases downstream) and is in a less favorable nucleic acid sequence contextthan the downstream ATG, relative to the ideal sequence postulated for efficientinitiation of translation. ...