Translation initiation on mammalian mRNAs with structured 5\'UTRs requires DExH-Box protein DHX29 (Cell, 2008, 135:1237-1250)

報告日期: 2009/05/19
報告時間: 17:05/18:55
報告學生: 石聿恒
講評老師: 曾大千

Translation Initiation on Mammalian mRNAs with Structured 5’UTRs Requires DExH-Box Protein DHX29

Vera P. Pisareva, Andrey V. Pisarev, Anton A. Komar, Christopher U.T. Hellen and Tatyana V. Pestova

Cell 2008 135:1237-1250


Speaker: Yu-Heng Shih

Commentator: Dr. Ta-Chien Tseng

Date/Time: 2009/05/19, 17:00~17:50

Place: Room 602, College of medicine



In most eukaryotes, the 48S initiation complexes assemble and recruit for translational initiation to the start codon of mRNA. 48S complex formation on most cellular mRNAs occurs by the scanning mechanism and requires at least seven initiation factors (eIFs: eIF2/3/1/1A/4A/4B/4F). 43S complexes (including 40S ribosomal subunit, Met-tRNAMeti and other eIFs) first attach to the 5’-proximal region of mRNA and then scan along the 5’ untranslated region (5’UTR) to the initiation codon. Ribosomal scanning consists of two linked processes: unwinding of secondary structure in the 5’UTR and ribosomal movement along it. It is clear that scanning requires ATP-dependent unwinding of RNA secondary structure by eIF4A/4G/4B and induction by eIF1/1A of the scanning competent conformation of 43S complexes. However, in author’s in vitro reconstituted initiation system containing seven initiation factors, 48S complexes did not form efficiently on mRNAs containing GC-rich stems of even moderate stability in their 5’UTRs, although they are translated well in cell-free extracts (rabbit reticulocyte lysate, RRL). This result indicates that additional factors may present in RRL. They therefore undertook extensive purification from RRL of a missing factor(s) required for efficient 48S complex formation on mRNAs with structured 5’UTRs. Purification yielded an apparently homogeneous ~150 kDa protein that was identified as DExH-box protein DHX29 by mass spectrometry. In toeprinting assay, they proved that DHX29 promote efficient 48S complex formation. The author also found DHX29 specifically binds to 40S ribosome subunits and stimulates 48S complex formation by hydrolyzing NTP.



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