ABSTRACT
Although Archaea are prokaryotic and resemble Bacteria morphologically, their transcription apparatus is remarkably similar to those of eukaryotic cell nuclei. Because some Archaea exist in environments with temperatures of around 100 degreesC, they are likely to have evolved unique strategies for transcriptional control. Here, we investigate the effects of temperature and DNA template topology in a thermophilic archaeal transcription system. Significantly, and in marked contrast with characterized eucaryal systems, archaeal DNA template topology has negligible effect on transcription levels at physiological temperatures using highly purified polymerase and recombinant transcription factors. Furthermore, archaeal transcription does not require hydrolysis of the beta-gamma phosphoanhydride bond of ATP. However, at lower temperatures, negatively supercoiled templates are transcribed more highly than those that are positively supercoiled. Notably, the block to transcription on positively supercoiled templates at lowered temperatures is at the level of polymerase binding and promoter opening. These data imply that Archaea do not possess a functional homologue of transcription factor TFIIH, and that for the promoters studied, transcription is mediated by TATA box-binding protein, transcription factor TFB, and RNA polymerase alone. Furthermore, they suggest that the reduction of plasmid linking number by hyperthermophilic Archaea in vivo in response to cold shock is a mechanism to maintain gene expression under these adverse circumstances.
Subject(s)
Archaea/genetics , DNA-Binding Proteins/metabolism , Sulfolobus/genetics , Transcription Factors, TFII , Transcription, Genetic , Archaea/metabolism , Base Sequence , DNA Footprinting , DNA, Superhelical/genetics , Deoxyribonuclease I , Plasmids , Promoter Regions, Genetic , Sulfolobus/metabolism , TATA Box , TATA-Box Binding Protein , Temperature , Templates, Genetic , Transcription Factor TFIIH , Transcription Factors/metabolismSubject(s)
Archaea/genetics , Promoter Regions, Genetic , RNA Polymerase II/metabolism , Transcription Factors, TFII/metabolism , Transcription Factors/metabolism , Transcription, Genetic , Archaea/enzymology , Base Sequence , DNA, Archaeal/chemistry , DNA, Archaeal/genetics , Gene Expression Regulation, Archaeal , Models, Genetic , Models, Molecular , Nucleic Acid Conformation , Protein Conformation , Protein Structure, Secondary , TATA Box , Transcription Factor TFIID , Transcription Factors/chemistry , Transcription Factors, TFII/chemistryABSTRACT
Archaea possess a basal transcriptional apparatus that resembles that of eukaryotes. Here we report the 2.1-A crystal structure of the archaeal transcription factor complex formed by the TATA-box-binding protein (TBP), the transcription factor IIB homolog, and a DNA target, all from the hyperthermophile Pyrococcus woesei. The overall fold of these two basal transcription factors is essentially the same as that of their eukaryotic counterparts. However, in comparison with the eukaryotic complexes, the archaeal TBP-DNA interface is more symmetrical, and in this structure the orientation of the preinitiation complex assembly on the promoter is inverted with respect to that seen in all crystal structures of comparable eukaryotic systems. This study of the structural details of an archaeal transcription factor complex presents the opportunity to examine the evolution of the basal eukaryotic transcriptional apparatus from a stereochemical viewpoint and to extend our understanding of the physical biochemistry of transcriptional initiation.
