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Nucleic Acids Res. 2019 Jul 12. pii: gkz595. doi: 10.1093/nar/gkz595. [Epub ahead of print]

Functional interplay between DEAD-box RNA helicases Ded1 and Dbp1 in preinitiation complex attachment and scanning on structured mRNAs in vivo.

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Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Monash Bioinformatics Platform, Monash University, Clayton, VIC 3800, Australia.
EMBL-Australia Collaborating Group, Department of Genome Sciences, The John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2601, Australia.
Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia.


RNA structures that impede ribosome binding or subsequent scanning of the 5'-untranslated region (5'-UTR) for the AUG initiation codon reduce translation efficiency. Yeast DEAD-box RNA helicase Ded1 appears to promote translation by resolving 5'-UTR structures, but whether its paralog, Dbp1, performs similar functions is unknown. Furthermore, direct in vivo evidence was lacking that Ded1 or Dbp1 resolves 5'-UTR structures that impede attachment of the 43S preinitiation complex (PIC) or scanning. Here, profiling of translating 80S ribosomes reveals that the translational efficiencies of many more mRNAs are reduced in a ded1-ts dbp1Δ double mutant versus either single mutant, becoming highly dependent on Dbp1 or Ded1 only when the other helicase is impaired. Such 'conditionally hyperdependent' mRNAs contain unusually long 5'-UTRs with heightened propensity for secondary structure and longer transcript lengths. Consistently, overexpressing Dbp1 in ded1 cells improves the translation of many such Ded1-hyperdependent mRNAs. Importantly, Dbp1 mimics Ded1 in conferring greater acceleration of 48S PIC assembly in a purified system on mRNAs harboring structured 5'-UTRs. Profiling 40S initiation complexes in ded1 and dbp1 mutants provides direct evidence that Ded1 and Dbp1 cooperate to stimulate both PIC attachment and scanning on many Ded1/Dbp1-hyperdependent mRNAs in vivo.


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