title: L-Myc protein synthesis is initiated by internal ribosome entry.
abstract: An internal ribosome entry segment (IRES) has been identified in the 5' untranslated region (5' UTR) of two members of the myc family of proto-oncogenes, c-myc and N-myc. Hence, the synthesis of c-Myc and N-Myc polypeptides can involve the alternative mechanism of internal initiation. Here, we show that the 5' UTR of L-myc, another myc family member, also contains an IRES. Previous studies have shown that the translation of mRNAs containing the c-myc and N-myc IRESs can involve both cap-dependent initiation and internal initiation. In contrast, the data presented here suggest that internal initiation can account for all of the translation initiation that occurs on an mRNA with the L-myc IRES in its 5' UTR. Like many other cellular IRESs, the L-myc IRES appears to be modular in nature and the entire 5' UTR is required for maximum IRES efficiency. The ribosome entry window within the L-myc IRES is located some distance upstream of the initiation codon, and thus, this IRES uses a "land and scan" mechanism to initiate translation. Finally, we have derived a secondary structural model for the IRES. The model confirms that the L-myc IRES is highly structured and predicts that a pseudoknot may form near the 5' end of the mRNA.
authors.affiliation: Department of Biochemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Jopling
authors.forename: Keith A
authors.initials: KA
authors.lastname: Spriggs
authors.forename: Sally A
authors.initials: SA
authors.lastname: Mitchell
authors.forename: Mark
authors.initials: M
authors.lastname: Stoneley
authors.forename: Anne E
authors.initials: AE
authors.lastname: Willis
mesh_terms: D020121:5' Untranslated Regions / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger