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.
Steel
L F
LF
Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA. L-Steel@lac.jci.tju.edu
Telly
D L
DL
Leonard
J
J
Rice
B A
BA
Monks
B
B
Sawicki
J A
JA
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