Biomedical subjects

M Thomm

Publications and source records attributed to M Thomm.

At least 37 records · Page 2Linked to original sources

PubMed1996

Two transcription factors related with the eucaryal transcription factors TATA-binding protein and transcription factor IIB direct promoter recognition by an archaeal RNA polymerase.

We reported previously that cell-free transcription in the Archaea Methanococcus and Pyrococcus depends upon two archaeal transcription factors, archaeal transcription factor A (aTFA) and archaeal transcription factor B (aTFB). In the genome of Pyrococcus genes encoding putative homologues of eucaryal transcription factors TATA-binding protein (TBP) and TFIIB have been detected. Here, we report that Escherichia coli synthesized Pyrococcus homologues of TBP and TFIIB are able to replace endogenous aTFB and aTFA in cell-free transcription reactions. Antibodies raised against archaeal TBP and TFIIB bind to polypeptides of identical molecular mass in the aTFB and aTFA fraction. These data identify aTFB as archaeal TBP and aTFA as the archaeal homologue of TFIIB. At the Pyrococcus glutamate dehydrogenase (gdh) promoter these two bacterially produced transcription factors and endogenous RNA polymerase are sufficient to direct accurate and active initiation of transcription. DNase I protection experiments revealed Pyrococcus-TBP producing a characteristic footprint between position -20 and -34 centered around the TATA box of gdh promoter. Pyrococcus-TFIIB did not bind to the TATA box but bound cooperatively with Pyrococcus-TBP generating an extended DNase I footprinting pattern ranging from position -19 to -42. These data suggest that the Pyrococcus homologue of TFIIB associates with the TBP-promoter binary complex as its eucaryal counterpart, but in contrast to eucaryal TFIIB, it causes an extension of the protection to the region upstream of the TATA box.

Archaea↗

PubMed1996

A cell-free transcription system for the hyperthermophilic archaeon Pyrococcus furiosus.

We describe here the establishment of a cell-free transcription system for the hyperthermophilic Archaeon Pyrococcus furiosus using the cloned glutamate dehydrogenase (gdh) gene as template. The in vitro system that operated up to a temperature of 85 degrees C initiated transcription 23 bp downstream of a TATA box located 45 bp upstream of the translational start codon of gdh mRNA, at the same site as in Pyrococcus cells. Mutational analyses revealed that this TATA box is essential for in vitro initiation of transcription. Pyrococcus transcriptional components were separated into at least two distinct transcription factor activities and RNA polymerase. One of these transcription factors could be functionally replaced by Methanococcus aTFB and Thermococcus TATA bind- ing protein (TBP). Immunochemical analyses demonstrated a structural relationship between Pyrococcus aTFB and Thermococcus TBP. These findings indicate that a TATA box and a TBP are essential components of the Pyrococcus transcriptional machinery.

Archaea↗

PubMed1996

Archaeal transcription factors and their role in transcription initiation.

Archaeal RNA polymerases show a weak ability in vitro to bind to promoter DNA and/or to initiate transcription with low activity independent of upstream regulatory DNA sequences. Active transcription in vitro and in vivo, however, depends strictly on a TATA box resembling the TATA box of eucaryal polII promoters. This TATA box is recognized by a polypeptide related to eucaryal TATA-binding protein (TBP) that was formerly designated aTFB. Template competition studies showed that this archaeal TATA-binding protein (aTBP) is stably sequestered at the promoter by interaction with the second archaeal transcription factor, aTFA, which is related to eucaryal transcription factor IIB (TFIIB). The association of archaeal TFIIB (aTFIIB) with the aTBP-promoter complex leads to template commitment, indicating that aTFIIB recruits archaeal RNA polymerase to the preinitiation complex. These analyses suggest the following order for assembly of transcription factors on the archaeal promoter: aTBP, aTFIIB, RNA polymerase, and provide evidence for a common molecular mechanism of transcription initiation by eucaryal RNA polymerase II and archaeal RNA polymerases. The sequence of the genes encoding aTBP and aTFIIB (TFB) showed all the characteristics conserved in their eucaryal counterparts. The degree of sequence similarity between archaeal and eucaryal transcription factors is between 27 to 35% for TFIIB and between 36 to 41% for TBP. The findings discussed here indicate that TBP and TFIIB perform analogous functions in Archaea and Eucarya and show that four essential components of archaeal and eucaryal transcriptional machineries. RNA polymerase, TATA box, TBP and TFIIB are homologous.

Archaea↗

PubMed1995

Promoter recognition in archaea is mediated by transcription factors: identification of transcription factor aTFB from Methanococcus thermolithotrophicus as archaeal TATA-binding protein.

At least two transcription factors, aTFB and aTFA, are required for accurate and faithful in vitro transcription of homologous templates in cell-free extracts from the methanogenic Archaeon Methanococcus thermolithotrophicus. We have recently shown that the function of aTFB can be replaced by eucaryal TATA-binding proteins. Here we demonstrate using template commitment experiments that promoter recognition in an Archaeon is mediated by transcription factors. The archaeal TATA box was identified as recognition site for binding of aTFB by gel shift analyses. aTFB binds also to the TATA box of adenovirus 2 major late promoter suggesting homology of eucaryal and archaeal TATA boxes. Our analyses provide evidence for a common molecular mechanism of transcription initiation by eucaryal RNA polymerases and archaeal RNA polymerase. They indicate also an evolutionary homology for aTFB and TBP.

Adenoviridae↗

PubMed1995

The translation product of the presumptive Thermococcus celer TATA-binding protein sequence is a transcription factor related in structure and function to Methanococcus transcription factor B.

A gene for a putative homolog of TATA-binding protein (TBP) from Thermococcus celer has been expressed in Escherichia coli, and the function of the purified recombinant protein was studied in a Methanococcus-derived cell-free transcription system. Thermococcus TBP can replace archaeal transcription factor B (aTFB) in cell-free transcription reactions. This transcriptional activation is TATA box-dependent and occurs both on tRNA(Val) and protein-encoding genes as templates indicating that Thermococcus TBP is a general transcription factor. Antibodies raised against Thermococcus TBP bind to Methanococcus aTFB and inhibit a TFB activity. These findings demonstrate that Thermococcus TBP (like eucaryal TBPs) can direct specific transcription from TATA boxes.

Archaea↗

PubMed1995

Functional interaction of yeast and human TATA-binding proteins with an archaeal RNA polymerase and promoter.

TATA boxes are common structural features of eucaryal class II and archaeal promoters. In addition, a gene encoding a polypeptide with sequence similarity to eucaryal TATA-binding protein (TBP) has recently been detected in Archaea, but its relationship to the archaeal transcription factors A (aTFA) and B (aTFB) was unclear. Here, we demonstrate that yeast and human TBP can substitute for aTFB in a Methanococcus-derived archaeal cell-free transcription system. Template-commitment studies show that eucaryal TBP is stably sequestered at the archaeal promoter and that this interaction is further stabilized in combination with aTFA. Binding studies revealed that recognition of an archaeal promoter by TBP involves specific binding to the TATA box. These findings demonstrate a common function of TBP and aTFB and imply a common evolutionary origin of eucaryal and archaeal transcriptional machinery.

Base Sequence↗

PubMed1993

Purification and characterization of a general transcription factor, aTFB, from the archaeon Methanococcus thermolithotrophicus.

We have recently shown that cell-free transcription of homologous templates from the archaeon Methanococcus thermolithotrophicus requires an archaeal transcription factor (aTFA) that separated from the RNA polymerase during phosphocellulose chromatography. We report here the identification and extensive purification of a second activity, aTFB, required for in vitro transcription. This activity copurified with RNA polymerase during initial chromatographic steps but was positively identified as a distinct transcription factor after Superdex 200 sizing chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the intensity of a M(r) = 28,000 polypeptide in silver-stained gels is correlated with transcription factor activity. The same polypeptide, when eluted from a denaturing polyacrylamide gel and subsequently renatured, showed the functional properties of the transcription factor. In conjunction with gel filtration and sedimentation studies, which indicated a molecular mass of 54,000 Da for the native protein, these results suggested that aTFB is a dimer with polypeptide chains of identical molecular mass. Functional studies with highly purified aTFB demonstrated that it is a general factor required for transcription of genes encoding tRNA and proteins.

Cell-Free System↗

PubMed1992

Transcription in vitro and in vivo of the 7S RNA gene associated with the ribosomal RNA operon in the hyperthermophilic archaeon Methanothermus fervidus.

The gene encoding the archaeal 7S RNA in the hyperthermophile Methanothermus fervidus is linked to a tRNA(Ser) and rRNA operon in the arrangement 5'-7S RNA-14nt-tRNA(Ser)-196nt-16S rRNA and the promoter directing transcription of this 7S RNA gene has now been identified. Initiation of transcription of the 7S RNA gene has been shown to occur both in vivo in M. fervidus and in vitro, using a Methanococcus thermolithotrophicus derived cell-free transcription system, at the first G residue within the initiator sequence ATGG, located 6 bp upstream of the 5' end of the 7S RNA coding region. Cotranscription of the 7S RNA and tRNA(Ser) has been demonstrated in vitro.

Base Sequence↗

PubMed1992

Cell-free transcription of the nifH1 gene of Methanococcus thermolithotrophicus indicates that promoters of archaeal nif genes share basic features with the methanogen consensus promoter.

The nifH1 gene of Methanococcus thermolithotrophicus, which encodes the putative dinitrogenase reductase of an archaeon, was accurately transcribed in a homologous cell-free transcription system. Extracts of cells grown with N2 or ammonia as nitrogen source initiated transcription at the nifH1 promoter with similar efficiencies. We confirmed that cells grown under non-N2-fixing conditions do not contain significant amounts of nifH1-specific mRNA. The levels of cell-free transcription initiation at the nifH1 promoter were similar to those observed at a tRNA promoter. The DNA sequence from -40 to +5 relative to the initiator nucleotide of nifH1 mRNA contained all the information required for promoter activity. A mutational analysis of this section of DNA demonstrated that a TATA box at -25 and the TTGT motif (initiator element) at the transcription start site are essential for cell-free transcription. These elements are similar to the structural determinants of a known tRNA promoter of Methanococcus. Mutation of a sequence, showing homology to the bacterial NifA site, which overlaps the transcription start site, did not affect promoter activity. Hence, cell-free transcription of the Methanococcus nifH1 gene is independent of upstream activator elements and does not require alternate cis-acting sequences that differ from the methanogen consensus promoter. These findings suggest that the activation of nif promoters is brought about by fundamentally different mechanisms in Archaea and bacteria.

Ammonia↗

PubMed1992

Transcription in vivo and in vitro of the histone-encoding gene hmfB from the hyperthermophilic archaeon Methanothermus fervidus.

Immediately upstream of the hmfB gene, in a DNA fragment cloned from Methanothermus fervidus, are two identical tandemly repeated copies of a 73-bp sequence that contain the sequence 5'TTTATATA, which conforms precisely to the consensus TATA box element proposed for methanogen promoters. By using this duplicated region as the template DNA and a cell-free transcription system derived from Methanococcus thermolithotrophicus, transcription in vitro was found to initiate at two identical sites 73 bp apart, each 25 bp downstream from a TATA box, thus providing strong evidence for the functional conservation of this transcriptional signal in two phylogenetically very diverse methanogens. Transcription of the hmfB gene in vivo in M. fervidus was found to occur at only one of these sites, and consistent with this observation, recloning and sequencing of this intergenic region after its amplification by the polymerase chain reaction demonstrated that the genome of M. fervidus contains only one copy of the 73-bp sequence upstream of the hmfB gene. Since the second copy of the 73-bp sequence, presumably generated artifactually during the original hmfB cloning, functioned equally well as a promoter in the M. thermolithotrophicus transcription system, all information needed by the heterologous RNA polymerase to initiate transcription accurately in vitro must be present within this sequence. The hmfB gene encodes HMf-2, one of the two subunits of HMf, an abundant DNA binding protein in M. fervidus which binds to DNA molecules in vitro, forming nucleosomelike structures. Cell-free transcription was inhibited by adding HMf or eucaryotic core histones at protein-to-DNA mass ratios of 0.3:1 and 1:1, respectively, whereas the archael histonelike protein HTa from Thermoplasma acidophilum inhibited transcription in vitro only at much higher protein-to-DNA mass ratios and the bacterial histonelike protein HU from Escherichia coli had no detectable effect on transcription.

Archaeal Proteins↗

PubMed1991

Control regions of an archaeal gene. A TATA box and an initiator element promote cell-free transcription of the tRNA(Val) gene of Methanococcus vannielii.

To identify the DNA sequences required for initiation of transcription in archaea, the 5'-flanking region of the tRNA(Val) gene of Methanococcus vannielii was modified by deletions, restructuring and site-directed mutagenesis, and the tRNA encoding sequence was replaced by a fortuitous Escherichia coli sequence. The effects of these mutations on promoter function were tested in an homologous cell-free transcription system. The DNA region from position -35 to +9 relative to the transcription start site was sufficient for maximal initiation of cell-free transcription. Removal of the DNA region between -35 and -30 reduced initiation by a factor of 2. Deletions extending to position -24 almost completely abolished specific transcription. Analysis of 16 site-specific mutations in the region from -33 to +2 provided evidence that a conserved A + T-rich sequence (TATA box), centered at -25, is essential for initiation of transcription. Single point mutations in six positions of the TATA box reduced initiation of transcription from 0.2 to 0.01 of wild-type levels. A second conserved motif at the transcription start site (consensus ATGC) could be replaced by some sequences containing a pyrimidine-purine dinucleotide but appeared necessary for a maximal rate of gene transcription. Mutations altering the spacing between the two conserved elements demonstrated that initiation occurs at a strictly defined distance of 22 to 27 base-pairs downstream from the TATA box. Our results support the conclusion that the TATA box is the major DNA region mediating promoter recognition, influencing the efficiency of transcription and specifying the site of transcription initiation. This Methanococcus promoter element closely resembles in structure and function the TATA box of promoters of eukaryotic protein-encoding genes transcribed by RNA polymerase II.

Base Sequence↗

PubMed1990

An archaebacterial cell-free transcription system. The expression of tRNA genes from Methanococcus vannielii is mediated by a transcription factor.

Our understanding of the mechanism of RNA biosynthesis in archaebacteria is limited, due in part to the inability of purified RNA polymerases to transcribe purified genes accurately in vitro. In the present study, we show that cell extracts of Methanococcus vannielii and Methanococcus thermolithotrophicus purified by gradient centrifugation synthesize a distinct transcript from templates harboring a cloned homologous tRNA(Val) and tRNA(Arg) gene. The in vitro transcripts initiate with GTP at the same sites as in Methanococcus cells. About 60% of the sequence of the in vitro RNA products was analyzed by dideoxyterminated primer extension and found to be identical with that of the precursors of tRNA(Val) and tRNA(Arg). This finding indicates that this RNA polymerase fraction both initiates and terminates transcription faithfully in vitro. After purification of a cell-free extract (S-100) of M. thermolithotrophicus by phosphocellulose chromatography, the endogenous RNA polymerase has lost its ability to transcribe the tRNA(Val) gene accurately. The activity directing specific expression of this template was reconstituted by the addition of a protein-fraction devoid of RNA polymerase activity. Thus, a transcription factor appears to be required for accurate cell-free expression of tRNA genes from M. vannielii.

Base Sequence↗

PubMed1989

An archaebacterial promoter sequence assigned by RNA polymerase binding experiments.

To identify an archaebacterial promoter sequence, nuclease protection studies with the purified RNA polymerase of Methanococcus vannielii were performed. The enzyme binds specifically both at protein-encoding (hisA and methyl CoM reductase, component C) and tRNA-rRNA genes. The binding region of the RNA polymerase extends from 30 base pairs (bp) upstream (-30) to 20 bp downstream (+20) from the in vivo transcription start site. This finding indicates that the archaebacterial enzyme recognizes promoters without transacting transcription factors. The DNA segment protected from nuclease digestion by bound RNA polymerase contains an octanucleotide sequence centered at -25, which is conserved between the protein-encoding and the stable RNA genes. According to the specific binding of the enzyme to only DNA-fragments harbouring this motif, we propose the sequence TTTATATA as the major recognition signal of the Methanococcus RNA polymerase. Comparison of this motif with published archaebacterial DNA sequences revealed the presence of homologous sequences at the same location upstream of 36 genes. We therefore consider the overall consensus TTTATAATA as a general element of promoters in archaebacteria. In spite of the specific binding of the enzyme, most preparations of the Methanococcus vannielii RNA polymerase are unable to initiate transcription at the correct sites in vitro. Here we present first evidence for the possible existence of a transcription factor conferring the ability to the enzyme to initiate and terminate transcription specifically in vitro.

Archaea↗

PubMed1988

An archaebacterial RNA polymerase binding site and transcription initiation of the hisA gene in Methanococcus vannielii.

Transcription initiation of the hisA gene in vivo in the archaebacterium Methanococcus vannielii, as determined by nuclease S1 and primer extension analyses, occurs 73 base pairs (bp) upstream of the translation initiation site. Binding of M. vannielii RNA polymerase protects 43 bp of DNA, from 35 bp upstream (-35) to 8 bp downstream (+8) of the hisA mRNA initiation site, from digestion by DNase I and exonuclease III. An A + T rich region, with a sequence which conforms to the consensus sequence for promoters of stable RNA-encoding genes in methanogens, is found at the same location (-25) upstream of the polypeptide-encoding hisA gene. It appears therefore that a TATA-like sequence is also an element of promoters which direct transcription of polypeptide-encoding genes in this archaebacterium.

Bacterial Proteins↗

PubMed1988

An archaebacterial promoter element for stable RNA genes with homology to the TATA box of higher eukaryotes.

The RNA polymerase of Methanococcus vannielii, in binary complex with two stable RNA operons, protects from exonuclease digestion the region from 32 bp upstream (-32) to 18 bp downstream (+18) of the transcription start site. Contained within this binding region, centered at -25, is an AT-rich sequence which is highly conserved upstream of 26 other archaebacterial tRNA and rRNA genes. We therefore propose the sequence TTTATAATA as a common element of promoters for stable RNA genes in archaebacteria. Both the similarity in sequence and the location of this conserved octanucleotide suggest homology to the eukaryotic TATA box preceding protein encoding genes transcribed by RNA polymerase B.

Base Sequence↗

PubMed1988

RNA polymerase-binding and transcription initiation sites upstream of the methyl reductase operon of Methanococcus vannielii.

RNA polymerase, purified from Methanococcus vannielii, was shown by exonuclease III footprinting to bind to a 49-base-pair (bp) region of DNA in the intergenic region upstream of mcrB. S1 nuclease protection experiments demonstrated that transcription initiation in vivo occurs within this region at 32 or 33 bp 5' to the ATG translation initiation codon of mcrB and 19 or 20 bp 3' to a TATA box.

Base Sequence↗

PubMed1988

Cloning and physical mapping of RNA polymerase genes from Methanobacterium thermoautotrophicum and comparison of homologies and gene orders with those of RNA polymerase genes from other methanogenic archaebacteria.

The structural genes encoding the four largest subunits of RNA polymerase, A, B', B", and C, were physically mapped in Methanobacterium thermoautotrophicum Winter. The genes formed a cluster in the order B", B', A, C and had a common orientation. DNA hybridization experiments yielded different degrees of homology between RNA polymerase gene sequences of different species of Methanobacterium and Methanococcus voltae. No homology was detectable between Methanobacterium thermoautotrophicum and Methanosarcina barkeri. From Southern hybridization experiments in which probes of the four genes from Methanobacterium thermoautotrophicum Winter and restriction digests of the genomic DNAs of the different methanogens were used, a common gene order of the RNA polymerase genes could be deduced.

Archaea↗

PubMed1986

DNA-dependent RNA polymerases of the three orders of methanogens.

The DNA-dependent RNA polymerases of members of the three orders of methanogens were purified and their enzymatic properties described. The enzymes consist of 7-8 polypeptides. Although these differed in molecular mass, the four heaviest components could be allied to components of the enzyme of Methanobacterium thermoautotrophicum, W by cross-reaction with antibodies directed against the denatured polypeptides of this enzyme. The antisera against native RNA polymerases isolated from representatives of the different orders, on the other hand, gave rise to serological cross-reaction between different genera but not between different families and orders. These antisera are thus useful for taxonomic purposes. The RNA polymerase of the extreme thermophile Methanothermus fervidus shows a rather low thermostability. No factors having a stabilizing influence on the enzyme could be detected.

Cross Reactions↗