Elements in the murine c-mos messenger RNA 5'-untranslated region repress translation of downstream coding sequences.
Murine c-mos transcripts isolated from testes have 5'-untranslated regions (5'UTRs) of approximately 300 nucleotides with a series of four overlapping open reading frames (ORFs) upstream of the AUG codon that initiates the Mos ORF. Ovarian c-mos transcripts have shorter 5'UTRs (70-80 nucleotides) and contain only 1-2 of the upstream ORFs (uORFs). To test whether these 5'UTRs affect translational efficiency, we have constructed plasmids for the expression of chimeric transcripts with a mos-derived 5'UTR fused to the Escherichia coli beta-galactosidase coding region. Translational efficiency has been evaluated by measuring beta-galactosidase activity NIH3T3 cells transiently transfected with these plasmids and with plasmids where various mutations have been introduced into the 5'UTR. We show that the 5'UTR characteristic of testis-specific c-mos mRNA strongly represses translation relative to the translation of transcripts that contain a 5'UTR derived from beta-globin mRNA, and this is mainly due to the four uORFs. Each of the four upstream AUG triplets can be recognized as a start site for translation, and no single uAUG dominates the repressive effect. The uORFs repress translation by a mechanism that is not affected by the amino acid sequence in the COOH-terminal region of the uORF-encoded peptides. The very short uORF (AUGUGA) present in ovary-specific transcripts does not repress translation. Staining of testis sections from transgenic mice carrying chimeric beta-galactosidase transgene constructs, which contain a mos 5'UTR with or without the uATGs, suggests that the uORFs can dramatically change the pattern of expression in spermatogenic cells.
Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA. L-Steel@lac.jci.tju.edu
L F
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Steel
D L
DL
Telly
J
J
Leonard
B A
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Rice
B
B
Monks
J A
JA
Sawicki
D000818:Animals; D002460:Cell Line; D016258:Genes, mos; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D013737:Testis
D012333:RNA, Messenger