RESUMO
The structure of an RNA polymerase II/general transcription factor TFIIF complex was determined by cryo-electron microscopy and single particle analysis. Density due to TFIIF was not concentrated in one area but rather was widely distributed across the surface of the polymerase. The largest subunit of TFIIF interacted with the dissociable Rpb4/Rpb7 polymerase subunit complex and with the mobile "clamp." The distribution of the second largest subunit of TFIIF was very similar to that previously reported for the sigma subunit in the bacterial RNA polymerase holoenzyme, consisting of a series of globular domains extending along the polymerase active site cleft. This result indicates that the second TFIIF subunit is a true structural homolog of the bacterial sigma factor and reveals an important similarity of the transcription initiation mechanism between bacteria and eukaryotes. The structure of the RNAPII/TFIIF complex suggests a model for the organization of a minimal transcription initiation complex.
Assuntos
RNA Polimerase II/química , RNA Polimerase II/ultraestrutura , Fatores de Transcrição TFII/química , Fatores de Transcrição TFII/ultraestrutura , Sítio de Iniciação de Transcrição/fisiologia , Animais , Evolução Molecular , Humanos , Substâncias Macromoleculares , Microscopia Eletrônica , Modelos Moleculares , Estrutura Molecular , Filogenia , Regiões Promotoras Genéticas/fisiologia , Subunidades Proteicas/química , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/ultraestrutura , LevedurasAssuntos
RNA Polimerase II/química , RNA Polimerase II/metabolismo , Domínio Catalítico , Estrutura Molecular , Estrutura Quaternária de Proteína , Subunidades Proteicas , RNA Fúngico/biossíntese , RNA Fúngico/genética , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/metabolismo , Transcrição GênicaRESUMO
An 18 A resolution structure of the 12-subunit yeast RNA polymerase II (RNAPII) calculated from electron microscope images of single particles preserved in amorphous ice reveals the conformation of the enzyme in solution. The Rpb4/Rpb7 polymerase subunit complex was localized and found to be ideally positioned to determine the path of the nascent RNA transcript. The RNAPII structure suggests a revised mode of interaction with promoter DNA and demonstrates that regulation of RNAPII must involve structural changes that render the enzyme competent for initiation.
