scholarly journals Molecular architecture of 40S initiation complexes on the Hepatitis C virus IRES: from ribosomal attachment to eIF5B-mediated reorientation of initiator tRNA

2021 ◽  
Author(s):  
Zuben P. Brown ◽  
Irina S. Abaeva ◽  
Swastik De ◽  
Christopher U.T. Hellen ◽  
Tatyana V. Pestova ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Conformational Changes ◽  
Dynamic Network ◽  
Molecular Architecture ◽  
Entry Site ◽  
Internal Ribosome Entry ◽  
Initiation Factors ◽  
Direct Binding ◽  
Subunit Joining

Hepatitis C virus mRNA contains an internal ribosome entry site (IRES) that mediates end-independent translation initiation, requiring a subset of eukaryotic initiation factors (eIFs). Direct binding of the IRES to the 40S subunit places the initiation codon into the P site, where it base-pairs with eIF2-bound Met-tRNAiMet forming a 48S initiation complex. Then, eIF5 and eIF5B mediate subunit joining. Initiation can also proceed without eIF2, in which case Met-tRNAiMet is recruited directly by eIF5B. Here, we present cryo-EM structures of IRES initiation complexes at resolutions up to 3.5 Å that cover all major stages from initial ribosomal association, through eIF2-containing 48S initiation complexes, to eIF5B-containing complexes immediately prior to subunit joining. These structures provide insights into the dynamic network of 40S/IRES contacts, highlight the role for IRES domain II, and reveal conformational changes that occur during the transition from eIF2- to eIF5B-containing 48S complexes that prepare them for subunit joining.

scholarly journals Differential Effects on the Hepatitis C Virus (HCV) Internal Ribosome Entry Site by Vitamin B12 and the HCV Core Protein

2004 ◽  
Vol 78 (21) ◽  
pp. 12075-12081 ◽  
Author(s):  
Dongsheng Li ◽  
William B. Lott ◽  
John Martyn ◽  
Gholamreza Haqshenas ◽  
Eric J. Gowans
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Internal Ribosome Entry Site ◽  
Core Protein ◽  
Vitamin B ◽  
Entry Site ◽  
Internal Ribosome Entry ◽  
Hcv Core Protein ◽  
Hcv Ires

ABSTRACT To investigate the role of the hepatitis C virus internal ribosome entry site (HCV IRES) domain IV in translation initiation and regulation, two chimeric IRES elements were constructed to contain the reciprocal domain IV in the otherwise HCV and classical swine fever virus IRES elements. This permitted an examination of the role of domain IV in the control of HCV translation. A specific inhibitor of the HCV IRES, vitamin B12, was shown to inhibit translation directed by all IRES elements which contained domain IV from the HCV and the GB virus B IRES elements, whereas the HCV core protein could only suppress translation from the wild-type HCV IRES. Thus, the mechanisms of translation inhibition by vitamin B12 and the core protein differ, and they target different regions of the IRES.

scholarly journals La Autoantigen Is Necessary for Optimal Function of the Poliovirus and Hepatitis C Virus Internal Ribosome Entry Site In Vivo and In Vitro

2004 ◽  
Vol 24 (15) ◽  
pp. 6861-6870 ◽  
Author(s):  
Mauro Costa-Mattioli ◽  
Yuri Svitkin ◽  
Nahum Sonenberg
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Internal Ribosome Entry Site ◽  
Ribosomal Subunit ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Entry Site ◽  
Internal Ribosome Entry

ABSTRACT Translation of poliovirus and hepatitis C virus (HCV) RNAs is initiated by recruitment of 40S ribosomes to an internal ribosome entry site (IRES) in the mRNA 5′ untranslated region. Translation initiation of these RNAs is stimulated by noncanonical initiation factors called IRES trans-activating factors (ITAFs). The La autoantigen is such an ITAF, but functional evidence for the role of La in poliovirus and HCV translation in vivo is lacking. Here, by two methods using small interfering RNA and a dominant-negative mutant of La, we demonstrate that depletion of La causes a dramatic reduction in poliovirus IRES function in vivo. We also show that 40S ribosomal subunit binding to HCV and poliovirus IRESs in vitro is inhibited by a dominant-negative form of La. These results provide strong evidence for a function of the La autoantigen in IRES-dependent translation and define the step of translation which is stimulated by La.

scholarly journals Cell Type-Specific Enhancement of Hepatitis C Virus Internal Ribosome Entry Site-Directed Translation due to 5′ Nontranslated Region Substitutions Selected during Passage of Virus in Lymphoblastoid Cells

2000 ◽  
Vol 74 (15) ◽  
pp. 7024-7031 ◽  
Author(s):  
Hervé Lerat ◽  
Yoko K. Shimizu ◽  
Stanley M. Lemon
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Cell Lines ◽  
Internal Ribosome Entry Site ◽  
Nucleotide Substitutions ◽  
Entry Site ◽  
Lymphoblastoid Cells ◽  
Internal Ribosome Entry ◽  
Translational Activity ◽  
Nontranslated Region

ABSTRACT Low-level replication of hepatitis C virus (HCV) in cultured lymphoblastoid cells inoculated with H77 serum inoculum led to the appearance of new virus variants containing identical substitutions at three sites within the viral 5′ nontranslated RNA (5′NTR): G107→A, C204→A, and G243→A (N. Nakajima, M. Hijikata, H. Yoshikura, and Y. K. Shimizu, J. Virol. 70:3325–3329, 1996). These results suggest that virus with this 5′NTR sequence may have a greater capacity for replication in such cells, possibly due to more efficient cap-independent translation, since these nucleotide substitutions reside within the viral internal ribosome entry site (IRES). To test this hypothesis, we examined the translation of dicistronic RNAs containing upstream and downstream reporter sequences (Renilla and firefly luciferases, respectively) separated by IRES sequences containing different combinations of these substitutions. The activity of the IRES was assessed by determining the relative firefly and Renillaluciferase activities expressed in transfected cells. Compared with the IRES present in the dominant H77 quasispecies, an IRES containing all three nucleotide substitutions had significantly greater translational activity in three of five human lymphoblastoid cell lines (Raji, Bjab, and Molt4 but not Jurkat or HPBMa10-2 cells). In contrast, these substitutions did not enhance IRES activity in cell lines derived from monocytes or granulocytes (HL-60, KG-1, or THP-1) or hepatocytes (Huh-7) or in cell-free translation assays carried out with rabbit reticulocyte lysates. Each of the three substitutions was required for maximally increased translational activity in the lymphoblastoid cells. The 2- to 2.5-fold increase in translation observed with the modified IRES sequence may facilitate the replication of HCV, possibly accounting for differences in quasispecies variants recovered from liver tissue and peripheral blood mononuclear cells of the same patient.

scholarly journals The Ribosome Binding Site of Hepatitis C Virus mRNA

2001 ◽  
Vol 75 (16) ◽  
pp. 7629-7636 ◽  
Author(s):  
J. Robin Lytle ◽  
Lily Wu ◽  
Hugh D. Robertson
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Binding Site ◽  
Ribosome Binding Site ◽  
Entry Site ◽  
Internal Ribosome Entry ◽  
Ribosome Binding ◽  
Ribosome Binding Sites ◽  
Promising Target ◽  
Hcv Ires

ABSTRACT Hepatitis C virus (HCV) infects an estimated 170 million people worldwide, the majority of whom develop a chronic infection which can lead to severe liver disease, and for which no generally effective treatment yet exists. A promising target for treatment is the internal ribosome entry site (IRES) of HCV, a highly conserved domain within a highly variable RNA. Never before have the ribosome binding sites of any IRES domains, cellular or viral, been directly characterized. Here, we reveal that the HCV IRES sequences most closely associated with 80S ribosomes during protein synthesis initiation are a series of discontinuous domains together comprising by far the largest ribosome binding site yet discovered.

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