Browsing by Author "Schell, Stephanie"

Poly(A)-specific ribonuclease (DARN) is a processive 3'-exoribonuclease involved in the decay of eukaryotic mRNAs. Interestingly, PARN interacts clot only with the 3' end of the mRNA but also with its 5' end as PARN contains an RRM domain that specifically binds both the poly(A) tail and the 7-methylguanosine (m(7)G) cap. The interaction of PARK with the 5' cap of mRNAs stimulates the deadenylation activity and enhances the processivity of this reaction. We have determined the crystal structure of the PARN-RRM domain with a bound m G triphosphate nucleotide, revealing a novel binding mode for the m7G cap. The structure of the m(7)G binding pocket is located outside of the canonical RNA-binding surface of the RRM domain and differs significantly from that of other m(7)G-cap-binding proteins. The crystal structure also shows a remarkable conformational flexibility of the RRM domain, leading to a perfect exchange of two alpha-helices with an adjacent protein molecule in the crystal lattice. (C) 2008 Elsevier Ltd. All rights reserved.

The multisubunit eukaryotic translation initiation factor 3, among which the subunit b (eIF3b) is a major scaffold protein, plays essential roles in protein synthesis. Here, we report the crystal structure of the WD40 domain of Chaetomium thermophilum eIF3b, revealing a nine-bladed beta-propeller fold. Sequence analysis indicates that this propeller architecture is common to all eIF3b orthologs. Revisiting the cryo-electron microscopy (cryo-EM) map of the 43S preinitiation complex suggests an interaction of the eIF3b with the 40S ribosomal subunit involving the ribosomal protein S9e and the 18S rRNA. This model is strongly supported by the direct binding of eIF3b to 40S ribosomes and to the isolated ribosomal protein rpS9e in vitro.