RESUMO
Eukaryotic translation initiation requires the recruitment of the large, multiprotein eIF3 complex to the 40S ribosomal subunit. We present X-ray structures of all major components of the minimal, six-subunit Saccharomyces cerevisiae eIF3 core. These structures, together with electron microscopy reconstructions, cross-linking coupled to mass spectrometry, and integrative structure modeling, allowed us to position and orient all eIF3 components on the 40Sâ eIF1 complex, revealing an extended, modular arrangement of eIF3 subunits. Yeast eIF3 engages 40S in a clamp-like manner, fully encircling 40S to position key initiation factors on opposite ends of the mRNA channel, providing a platform for the recruitment, assembly, and regulation of the translation initiation machinery. The structures of eIF3 components reported here also have implications for understanding the architecture of the mammalian 43S preinitiation complex and the complex of eIF3, 40S, and the hepatitis C internal ribosomal entry site RNA.
Assuntos
Fator de Iniciação 1 em Eucariotos/química , Fator de Iniciação 3 em Eucariotos/química , Iniciação Traducional da Cadeia Peptídica , Subunidades Ribossômicas Menores de Eucariotos/química , Proteínas de Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/química , Sequência de Aminoácidos , Animais , Cristalografia por Raios X , Dimerização , Fator de Iniciação 1 em Eucariotos/metabolismo , Fator de Iniciação 3 em Eucariotos/metabolismo , Hepacivirus/química , Humanos , Mamíferos/metabolismo , Microscopia Eletrônica , Modelos Moleculares , Dados de Sequência Molecular , Ribonucleoproteínas/química , Subunidades Ribossômicas Menores de Eucariotos/metabolismo , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Alinhamento de SequênciaRESUMO
Eukaryotic translation initiation requires cooperative assembly of a large protein complex at the 40S ribosomal subunit. We have resolved a budding yeast initiation complex by cryo-EM, allowing placement of prior structures of eIF1, eIF1A, eIF3a, eIF3b and eIF3c. Our structure highlights differences in initiation-complex binding to the ribosome compared to that of mammalian eIF3, demonstrates a direct contact between eIF3j and eIF1A and reveals the network of interactions between eIF3 subunits.