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Translation initiation mediated by nuclear cap-binding protein complex
( Incheol Ryu ),( Yoon Ki Kim ) 생화학분자생물학회(구 한국생화학분자생물학회) 2017 BMB Reports Vol.50 No.4
In mammals, cap-dependent translation of mRNAs is initiated by two distinct mechanisms: cap-binding complex (CBC; a heterodimer of CBP80 and 20)-dependent translation (CT) and eIF4E-dependent translation (ET). Both translation initiation mechanisms share common features in driving cap- dependent translation; nevertheless, they can be distinguished from each other based on their molecular features and biological roles. CT is largely associated with mRNA surveillance such as nonsense-mediated mRNA decay (NMD), whereas ET is predominantly involved in the bulk of protein synthesis. However, several recent studies have demonstrated that CT and ET have similar roles in protein synthesis and mRNA surveillance. In a subset of mRNAs, CT preferentially drives the cap-dependent translation, as ET does, and ET is responsible for mRNA surveillance, as CT does. In this review, we summarize and compare the molecular features of CT and ET with a focus on the emerging roles of CT in translation. [BMB Reports 2017; 50(4): 186-193]
Ryu, Incheol,Kim, Yoon Ki American Society for Biochemistry and Molecular Bi 2019 The Journal of biological chemistry Vol.294 No.19
<P>Replication-dependent histone (RDH) mRNAs have a nonpolyadenylated 3′-UTR that ends in a highly conserved stem-loop structure. Nonetheless, a subset of RDH mRNAs has a poly(A) tail under physiological conditions. The biological meaning of poly(A)-containing (+) RDH mRNAs and details of their biosynthesis remain elusive. Here, using HeLa cells and Western blotting, qRT-PCR, and biotinylated RNA pulldown assays, we show that poly(A)<SUP>+</SUP> RDH mRNAs are post-transcriptionally regulated via adenylate- and uridylate-rich element–mediated mRNA decay (AMD). We observed that the rapid degradation of poly(A)<SUP>+</SUP> RDH mRNA is driven by butyrate response factor 1 (BRF1; also known as ZFP36 ring finger protein–like 1) under normal conditions. Conversely, cellular stresses such as UV C irradiation promoted BRF1 degradation, increased the association of Hu antigen R (HuR; also known as ELAV-like RNA-binding protein 1) with the 3′-UTR of poly(A)<SUP>+</SUP> RDH mRNAs, and eventually stabilized the poly(A)<SUP>+</SUP> RDH mRNAs. Collectively, our results provide evidence that AMD surveils poly(A)<SUP>+</SUP> RDH mRNAs via BRF1-mediated degradation under physiological conditions.</P>
Choe, Junho,Ryu, Incheol,Park, Ok Hyun,Park, Joori,Cho, Hana,Yoo, Jin Seon,Chi, Sung Wook,Kim, Min Kyung,Song, Hyun Kyu,Kim, Yoon Ki National Academy of Sciences 2014 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.111 No.43
<P>It has long been considered that intron-containing (spliced) mRNAs are translationally more active than intronless mRNAs (identical mRNA not produced by splicing). The splicing-dependent translational enhancement is mediated, in part, by the exon junction complex (EJC). Nonetheless, the molecular mechanism by which each EJC component contributes to the translational enhancement remains unclear. Here, we demonstrate the previously unappreciated role of eukaryotic translation initiation factor 4AIII (eIF4AIII), a component of EJC, in the translation of mRNAs bound by the nuclear cap-binding complex (CBC), a heterodimer of cap-binding protein 80 (CBP80) and CBP20. eIF4AIII is recruited to the 5'-end of mRNAs bound by the CBC by direct interaction with the CBC-dependent translation initiation factor (CTIF); this recruitment of eIF4AIII is independent of the presence of introns (deposited EJCs after splicing). Polysome fractionation, tethering experiments, and in vitro reconstitution experiments using recombinant proteins show that eIF4AIII promotes efficient unwinding of secondary structures in 5'UTR, and consequently enhances CBC-dependent translation in vivo and in vitro. Therefore, our data provide evidence that eIF4AIII is a specific translation initiation factor for CBC-dependent translation.</P>