eIF3-mediated ribosome recruitment by histone H4 mRNA during translation initiation
Résumé
The vast majority of eukaryotic mRNAs initiate translation through a canonical cap-dependent mechanism requiring a free 5’ cap and initiation factors (eIF) to form a translationally active ribosome. This tightly regulated process consists of several steps and involves 12 eIFs, 40S and 60S ribosomal subunits until the anticodon of tRNAMet is paired with the AUG codon into the P-site of the 80S ribosome.
We have shown that translation initiation of histone H4 mRNA combines canonical features (cap-dependent translation) with viral strategy (lack of scanning and internal recruitment of initiation factors)[1]. H4 mRNA contains a double stem-loop structure called eIF4E-sensitive element that recruits the cap-binding complex eIF4F. In addition, H4 mRNA contains a three-way junction that helps ribosome recruitment and positioning on the AUG start codon.
Recent PAR-CLIP experiments showed that eIF3 plays a crucial role in the selection and regulation of some characteristic cellular mRNAs, including histone mRNAs[2]. In this work, we decipher the interactions between histone mRNAs and eIF3. To this end we performed ribonucleoprotein immunoprecipitations using HEK293 extracts and showed that all histone mRNAs are able to interact in vivo with eIF3. By UV crosslinking experiments, we identified four eIF3 subunits able to interact with H4 mRNA: c, d, e and g. Next we performed GST-pulldown experiments on HEK293 total RNA using the four isolated subunits produced in E. coli. The mRNA of the linker histone H1 was found to bind tightly the four eIF3 subunits while the octameric core histone mRNAs (H2A, H2B, H3 and H4) interacted with the three subunits c, d, and g, but not eIF3e. Our results also highlighted a marked preference of H4 mRNA for eIF3d binding.
Altogether, the data suggest that eIF3 could play a significant role during translation initiation of histone mRNAs. Further investigations will address the effects of eIF3 down-regulation on histone synthesis in vivo.
Martin F., Barends S., Jaeger S., Schaeffer L., Prongidi-Fix L., Eriani G. (2011) Cap-assisted internal initiation of translation of histone H4. Mol Cell., 41, 197-209.
Lee AS., Kranzusch P., Cate J. (2015) eIF3 targets cell proliferation mRNAs for translational activation or repression. Nature, 522, 111-114.
Domaines
Biologie moléculaire
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