Novel Cytoplasmic Cap Binding Proteins in Yeast
The 5′ terminal cap structure, m7GpppX (where X is any nucleotide), is a ubiquitous feature of eukaryotic mRNAs that plays an important role in the cytoplasm and the nucleus. In the cytoplasm the cap structure enhances translational efficiency (Shatkin, 1985). In the nucleus, in vitro studies have demonstrated that the efficiency of mRNA splicing (Konarska et al, 1984;Edery and Sonenberg,1985), and 3′ end processing (Georgiev et al, 1984;Hart et al, 1985) is enhanced by the presence of a cap structure. Furthermore, the cap protects the mRNA against 5′ exonucleolytic degradation in both the nucleus and the cytoplasm (Furuichi et al,1977;Green et al, 1983) and is implicated in nucleocytoplasmic transport (Hamm and Mataj, 1990). Consistent with the role of the cap in nuclear events, recent data demonstrate that a significant portion of the cap binding protein (eIF-4E) is localized to the nucleus (Lejbkowicz et al,1992).
KeywordsCoat Protein Gene Disruption Covalent Bond Formation HeLa Nuclear Extract Protein Synthesis Initiation
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