Translational Control of the Xenopus laevisConnexin-41 5′-Untranslated Region by Three Upstream Open Reading Frames

• Published in: The Journal of biological chemistry 2000-10, Vol.275 (40), p.30787-30793
• Main Authors: Meijer, Hedda A., Dictus, Wim J.A.G., Keuning, Eelco D., Thomas, Adri A.M.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M005531200

The Xenopus laevis Connexin-41 (Cx41) mRNA contains three upstream open reading frames (uORFs) in the 5′-untranslated region (UTR). We analyzed the translation efficiency of constructs containing the Cx41 5′-UTR linked to the green fluorescent protein reporter after injection of transcripts into one-cell stageXenopus embryos. The translational efficiency of the wild-type Cx41 5′-UTR was only 2% compared with that of the β-globin 5′-UTR. Mutation of each of the three uAUGs into AAG codons enhanced translation 82-, 9-, and 4-fold compared with the wild-type Cx41 5′-UTR. Based on these increased translation efficiencies, the percentages of ribosomes that recognized the uAUGs were calculated. Only 0.03% of the ribosomes that entered at the cap structure scanned the entire 5′-UTR and translated the main ORF. The results indicate that all uAUGs are recognized by the majority of the scanning ribosomes and that the three uAUGs strongly modulate translation efficiency inXenopus laevis embryos. Based on these data, a model of ribosomal flow along the mRNA is postulated. We conclude that the three uORFs may play an important role in the regulation of Cx41 expression.