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Translation of the human c-myc P0 tricistronic mRNA involves two independent internal ribosome entry sites
C Nanbru1, A C Prats, L Droogmans
1Laboratoire de Chimie Biologique, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, rue Profs Jeener et Brachet 12, 6041 Gosselies, Belgium.
Abstract:
The human c-myc proto-oncogene is transcribed from four alternative promoters (P0, P1, P2, and P3) giving rise to mRNAs having 5' leader sequences of various length. The c-myc P0 mRNA contains three open reading frames (ORFs), the last one encoding c-Myc1 and c-Myc2 proteins generated by alternative translation initiated at CUG and AUG codons. The middle ORF (MYCHEX1) and the 5' ORF (ORF1) code for proteins 188 and 114 amino acids in length, respectively. We and others previously identified an internal ribosome entry site (IRES) in P0 and P2 c-myc mRNAs, promoting the cap-independent translation of c-Myc1 and c-Myc2. Here, we report the presence of a second IRES (named IRES1) promoting the cap-independent translation of MYCHEX1 in c-myc P0 mRNA. Using deletion analysis, we mapped an 80-nt region essential for IRES1 activity. c-myc P0 mRNA is thus the first eukaryotic polycistronic mRNA described for which translation initiation of two different open reading frames (MYCHEX1 and c-Myc1/c-Myc2) involves internal ribosome entry.
Insights
The human c-myc proto-oncogene
Area of Science:
- Molecular Biology
- Gene Regulation
- Cancer Research
Background:
- The human c-myc proto-oncogene utilizes four promoters (P0, P1, P2, P3) generating mRNAs with diverse 5' leader sequences.
- The c-myc P0 mRNA contains three open reading frames (ORFs): ORF1, MYCHEX1, and the terminal ORFs encoding c-Myc1/c-Myc2.
- Internal ribosome entry sites (IRES) facilitate cap-independent translation of c-Myc1 and c-Myc2 from P0 and P2 c-myc mRNAs.
Purpose of the Study:
- To identify and characterize additional regulatory elements involved in the cap-independent translation of c-myc P0 mRNA.
- To investigate the mechanism of translation initiation for the MYCHEX1 open reading frame within the c-myc P0 mRNA.
- To determine if the c-myc P0 mRNA can support the translation of multiple proteins via internal ribosome entry.
Main Methods:
- Deletion analysis was employed to map the functional region responsible for internal ribosome entry.
- Reporter assays were used to assess the cap-independent translation activity of identified RNA elements.
- Bioinformatic tools and molecular biology techniques were utilized to analyze mRNA structure and protein expression.
Main Results:
- A second internal ribosome entry site (IRES1) was identified in the c-myc P0 mRNA.
- IRES1 promotes the cap-independent translation of the MYCHEX1 open reading frame.
- An 80-nucleotide region was mapped as essential for IRES1 activity.
Conclusions:
- The c-myc P0 mRNA represents the first described eukaryotic polycistronic mRNA utilizing internal ribosome entry for the translation of two distinct open reading frames.
- This finding expands our understanding of complex gene regulation mechanisms for proto-oncogenes.
- The discovery of IRES1 provides new insights into alternative translation strategies in eukaryotic gene expression.