The two upstream open reading frames of oncogene mdm2 have different translational regulatory properties.
Few details are known of the mechanisms through which multiple upstream open reading frames (uORFs) interact to regulate translation in higher eukaryotes. The predominant transcript of oncogene mdm2 in normal human cells (L-mdm2) contains two upstream open reading frames in its 5' leader. Elimination of these two uORFs raises the translational efficiency of the transcript by over 10-fold in HeLa cells. The 5'-most uORF (uORF1) alone suppresses downstream translational activity by over 5-fold, whereas uORF2 contributes <2-fold to the inhibition by the intact leader. The different activities of the two uORFs do not depend on the nucleotide sequence surrounding the uORFs in the 5' leader, the order of the two uORFs in the 5' leader, or the occurrence of secondary structure or rare codons within the uORFs. Specific features of the amino acid sequence encoded by uORF1 contribute to its stronger suppressive activity, suggesting that it belongs to the class of "sequence-specific" uORFs. The weaker inhibitory activity inherent in uORF2 is potentiated by a sub-optimal nucleotide context surrounding its initiator AUG. The occurrence of two uORFs with differing activities in both the human gene and the mouse orthologue suggests that this pair of elements may play a fundamental role in regulating expression of the mdm2 gene.
Jin
Xiaoping
X
Department of Biochemistry, University of Washington, Seattle, Washington 98195-7350, USA.
Turcott
Eileen
E
Englehardt
Silvia
S
Mize
Gregory J
GJ
Morris
David R
DR
D020121:5' Untranslated Regions / Q000378:metabolism; D000595:Amino Acid Sequence; D003062:Codon; D018387:Codon, Initiator; D017124:Conserved Sequence; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006367:HeLa Cells; D019382:Human Growth Hormone / Q000378:metabolism; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D016366:Open Reading Frames; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051736:Proto-Oncogene Proteins c-mdm2; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D020121:5' Untranslated Regions; D003062:Codon; D018387:Codon, Initiator; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D019382:Human Growth Hormone; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D012260:Ribonucleases