scholarly journals The dynein light chain LC8 is required for RNA polymerase I-mediated transcription inTrypanosoma brucei,facilitating assembly and promoter binding of class I transcription factor A

2015 ◽  
pp. MCB.00705-15 ◽  
Author(s):  
Justin K Kirkham ◽  
Sung Hee Park ◽  
Tu N Nguyen ◽  
Ju Huck Lee ◽  
Arthur Günzl
Keyword(s):  
Transcription Factor ◽  
Rna Polymerase ◽  
Light Chain ◽  
Antigenic Variation ◽  
Surface Glycoprotein ◽  
Class I ◽  
Dynein Light Chain ◽  
Pol I ◽  
Independent Functions

Dynein light chain LC8 is highly conserved among eukaryotes and has both dynein-dependent and dynein-independent functions. Interestingly, LC8 was identified as a subunit of the class I transcription factor A (CITFA), which is essential for transcription by RNA polymerase (pol) I in the parasiteTrypanosoma brucei.Given that LC8 has never been identified with a basal transcription factor and thatT. bruceirelies on RNA pol I for expressing the variant surface glycoprotein (VSG), the key protein in antigenic variation, we investigated the CITFA-specific role of LC8. Depletion of LC8 from mammalian-infective bloodstream trypanosomes affected cell cycle progression, reduced the abundances of rRNA andVSGmRNA, and resulted in rapid cell death. Sedimentation analysis, co-immunoprecipitation of recombinant proteins, and bioinformatic analysis revealed an LC8 binding site near the N-terminus of the subunit CITFA2. Mutation of this site prevented the formation of a CITFA2-LC8 heterotetramer and,in vivo, was lethal, affecting assembly of a functional CITFA complex. Gel shift assays and UV-crosslinking experiments identified CITFA2 as a promoter-binding CITFA subunit. Accordingly, silencing ofLC8orCITFA2resulted in a loss of CITFA from RNA pol I promoters. Hence, we discovered an LC8 interaction that, unprecedentedly, has a basal function in transcription.

scholarly journals Characterization of a Novel Class I Transcription Factor A (CITFA) Subunit That Is Indispensable for Transcription by the Multifunctional RNA Polymerase I of Trypanosoma brucei

2012 ◽  
Vol 11 (12) ◽  
pp. 1573-1581 ◽  
Author(s):  
Tu N. Nguyen ◽  
Bao N. Nguyen ◽  
Ju Huck Lee ◽  
Aswini K. Panigrahi ◽  
Arthur Günzl
Keyword(s):  
Transcription Factor ◽  
Rna Polymerase ◽  
Trypanosoma Brucei ◽  
Rna Polymerase I ◽  
Class I ◽  
Mammalian Host ◽  
Subunit Structure ◽  
Content Type ◽  
Pol I ◽  
Polymerase I

ABSTRACT Trypanosoma brucei is the only organism known to have evolved a multifunctional RNA polymerase I (pol I) system that is used to express the parasite's ribosomal RNAs, as well as its major cell surface antigens, namely, the variant surface glycoprotein (VSG) and procyclin, which are vital for establishing successful infections in the mammalian host and the tsetse vector, respectively. Thus far, biochemical analyses of the T. brucei RNA pol I transcription machinery have elucidated the subunit structure of the enzyme and identified the class I transcription factor A (CITFA). CITFA binds to RNA pol I promoters, and its CITFA-2 subunit was shown to be absolutely essential for RNA pol I transcription in the parasite. Tandem affinity purification (TAP) of CITFA revealed the subunits CITFA-1 to -6, which are conserved only among kinetoplastid organisms, plus the dynein light chain DYNLL1. Here, by tagging CITFA-6 instead of CITFA-2, a complex was purified that contained all known CITFA subunits, as well as a novel proline-rich protein. Functional studies carried out in vivo and in vitro , as well as a colocalization study, unequivocally demonstrated that this protein is a bona fide CITFA subunit, essential for parasite viability and indispensable for RNA pol I transcription of ribosomal gene units and the active VSG expression site in the mammalian-infective life cycle stage of the parasite. Interestingly, CITFA-7 function appears to be species specific, because expression of an RNA interference (RNAi)-resistant CITFA-7 transgene from Trypanosoma cruzi could not rescue the lethal phenotype of silencing endogenous CITFA-7 .

scholarly journals Promoter occupancy of the basal class I transcription factor A differs strongly between active and silent VSG expression sites in Trypanosoma brucei

2013 ◽  
Vol 42 (5) ◽  
pp. 3164-3176 ◽  
Author(s):  
Tu N. Nguyen ◽  
Laura S. M. Müller ◽  
Sung Hee Park ◽  
T. Nicolai Siegel ◽  
Arthur Günzl
Keyword(s):  
Transcription Factor ◽  
Rna Polymerase ◽  
Trypanosoma Brucei ◽  
Transcription Initiation ◽  
Rna Polymerase I ◽  
Surface Glycoprotein ◽  
Class I ◽  
Monoallelic Expression ◽  
Promoter Occupancy ◽  
Polymerase I

Abstract Monoallelic expression within a gene family is found in pathogens exhibiting antigenic variation and in mammalian olfactory neurons. Trypanosoma brucei, a lethal parasite living in the human bloodstream, expresses variant surface glycoprotein (VSG) from 1 of 15 bloodstream expression sites (BESs) by virtue of a multifunctional RNA polymerase I. The active BES is transcribed in an extranucleolar compartment termed the expression site body (ESB), whereas silent BESs, located elsewhere within the nucleus, are repressed epigenetically. The regulatory mechanisms, however, are poorly understood. Here we show that two essential subunits of the basal class I transcription factor A (CITFA) predominantly occupied the promoter of the active BES relative to that of a silent BES, a phenotype that was maintained after switching BESs in situ. In these experiments, high promoter occupancy of CITFA was coupled to high levels of both promoter-proximal RNA abundance and RNA polymerase I occupancy. Accordingly, fluorescently tagged CITFA-7 was concentrated in the nucleolus and the ESB. Because a ChIP-seq analysis found that along the entire BES, CITFA-7 is specifically enriched only at the promoter, our data strongly indicate that monoallelic BES transcription is activated by a mechanism that functions at the level of transcription initiation.

scholarly journals Quantification of RNA Polymerase I transcriptional attenuation at the active VSG expression site in Trypanosoma brucei

2021 ◽  
Author(s):  
Nadine Weisert ◽  
Klara Thein ◽  
Helena Reis ◽  
Christian J Janzen
Keyword(s):  
Rna Polymerase ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Rna Polymerase I ◽  
Surface Glycoprotein ◽  
Transcriptional Elongation ◽  
Pol I ◽  
Expression Site ◽  
Polymerase I ◽  
Large Repertoire

The cell surface of the extracellular pathogen Trypanosoma brucei consists of a dense coat of variant surface glycoprotein (VSG), which enables the parasite to evade the immune system of the vertebrate host. Only one VSG gene from a large repertoire is expressed from a so-called bloodstream form expression site (BES) at a given timepoint. There are several BES in every parasite but only one is transcriptionally active. Other BES are silenced by transcriptional attenuation. Periodic activation of a previously-silenced BES results in differential VSG transcription and escape from the immune response. A process called antigenic variation. In contrast to gene transcription in other eukaryotes, the BES is transcribed by RNA polymerase I (Pol I). It was proposed that this highly-processive polymerase is needed to provide a sufficiently high transcription rate at the VSG gene. Surprisingly, we discovered a position-dependent Pol I activity and attenuation of transcriptional elongation also at the active BES. Transcription rates at the VSG gene appear to be comparable to Pol II-mediated transcription of house-keeping genes. Although these findings are in contradiction to the long-standing concept of continuously high transcription rates at the active BES in Trypanosoma brucei, they are complementary to recent groundbreaking findings about transcriptional regulation of VSG genes.

Regulation of ndh expression in Escherichia coli by Fis

Microbiology ◽  
2004 ◽  
Vol 150 (2) ◽  
pp. 407-413 ◽  
Author(s):  
Laura Jackson ◽  
Timo Blake ◽  
Jeffrey Green
Keyword(s):  
Escherichia Coli ◽  
Transcription Factor ◽  
Rna Polymerase ◽  
Exponential Growth ◽  
Nadh Dehydrogenase ◽  
Class I ◽  
Nitrate Respiration ◽  
Anaerobic Conditions ◽  
Expression In Escherichia Coli

The Escherichia coli ndh gene encodes NADH dehydrogenase II, a primary dehydrogenase used during aerobic and nitrate respiration. The anaerobic transcription factor FNR represses ndh expression by binding at two sites centred at −94·5 and −50·5. In vivo transcription studies using promoter fusions with 5′ deletions confirmed that both FNR sites are required for maximum repression under anaerobic conditions. The histone-like protein Fis binds to three sites [centred at −123 (Fis I), −72, (Fis II) and +51 (Fis III)] in the ndh promoter. Using ndh : : lacZ promoter fusions carrying 5′ deletions, or replacement mutations it is shown that Fis III is a repressing site and that Fis I and II are activating sites, with the greatest contribution from Fis II. Deletion of the C-terminal domain of the RNA polymerase α-subunit abolished Fis-mediated activation of ndh expression, suggesting that ndh has a Class I Fis-activated promoter. In accordance with the established pattern of Fis synthesis, ndh transcription was greatest during exponential growth. Thus, it is suggested that Fis enhances ndh expression during periods of rapid growth, by acting as a Class I activator, and that the binding of tandem FNR dimers represses ndh expression by preventing interaction of the RNA polymerase α-subunit with DNA and Fis.

scholarly journals Nucleosomes Are Depleted at the VSG Expression Site Transcribed by RNA Polymerase I in African Trypanosomes

2009 ◽  
Vol 9 (1) ◽  
pp. 148-154 ◽  
Author(s):  
Luisa M. Figueiredo ◽  
George A. M. Cross
Keyword(s):  
Rna Polymerase ◽  
Antigenic Variation ◽  
Rna Polymerase I ◽  
Surface Glycoprotein ◽  
Micrococcal Nuclease ◽  
Rrna Genes ◽  
Host Immune System ◽  
African Trypanosomes ◽  
Pol I ◽  
Polymerase I

ABSTRACT In most eukaryotes, RNA polymerase I (Pol I) exclusively transcribes long arrays of identical rRNA genes (ribosomal DNA [rDNA]). African trypanosomes have the unique property of using Pol I to also transcribe the variant surface glycoprotein VSG genes. VSGs are important virulence factors because their switching allows trypanosomes to escape the host immune system, a mechanism known as antigenic variation. Only one VSG is transcribed at a time from one of 15 bloodstream-form expression sites (BESs). Although it is clear that switching among BESs does not involve DNA rearrangements and that regulation is probably epigenetic, it remains unknown why BESs are transcribed by Pol I and what roles are played by chromatin structure and histone modifications. Using chromatin immunoprecipitation, micrococcal nuclease digestion, and chromatin fractionation, we observed that there are fewer nucleosomes at the active BES and that these are irregularly spaced compared to silent BESs. rDNA coding regions are also depleted of nucleosomes, relative to the rDNA spacer. In contrast, genes transcribed by Pol II are organized in a more compact, regularly spaced, nucleosomal structure. These observations provide new insight on antigenic variation by showing that chromatin remodeling is an intrinsic feature of BES regulation.

The human RNA polymerase I structure reveals an HMG-like transcription factor docking domain specific to metazoans

2021 ◽  
Author(s):  
Julia L Daiß ◽  
Michael Pilsl ◽  
Kristina Straub ◽  
Andrea Bleckmann ◽  
Mona Höcherl ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Rna Polymerase ◽  
In Vitro Transcription ◽  
Cellular Growth ◽  
Hmg Box ◽  
Transcription Bubble ◽  
Transcription System ◽  
Pol I ◽  
Additional Domain

Transcription of the ribosomal RNA precursor by RNA polymerase (Pol) I is a major determinant of cellular growth and dysregulation is observed in many cancer types. Here, we present the purification of human Pol I from cells carrying a genomic GFP-fusion on the largest subunit allowing the structural and functional analysis of the enzyme across species. In contrast to yeast, human Pol I carries a single-subunit stalk and in vitro transcription indicates a reduced proofreading activity. Determination of the human Pol I cryo-EM reconstruction in a close-to-native state rationalizes the effects of disease-associated mutations and uncovers an additional domain that is built into the sequence of Pol I subunit RPA1. This "dock II" domain resembles a truncated HMG-box incapable of DNA-binding which may serve as a downstream-transcription factor binding platform in metazoans. Biochemical analysis and ChIP data indicate that Topoisomerase 2a can be recruited to Pol I via the domain and cooperates with the HMG-box domain containing factor UBF. These adaptations of the metazoan Pol I transcription system may allow efficient release of positive DNA supercoils accumulating downstream of the transcription bubble.

scholarly journals Heterogeneous nuclear ribonucleoprotein K is a transcription factor.

1996 ◽  
Vol 16 (5) ◽  
pp. 2350-2360 ◽  
Author(s):  
E F Michelotti ◽  
G A Michelotti ◽  
A I Aronsohn ◽  
D Levens
Keyword(s):  
Transcription Factor ◽  
Rna Polymerase ◽  
Rna Polymerase Ii ◽  
Hnrnp K ◽  
Heterogeneous Nuclear Ribonucleoprotein ◽  
Transcription In Vitro ◽  
Nuclear Ribonucleoprotein ◽  
Rna Polymerase Ii Transcription

The CT element is a positively acting homopyrimidine tract upstream of the c-myc gene to which the well-characterized transcription factor Spl and heterogeneous nuclear ribonucleoprotein (hnRNP) K, a less well-characterized protein associated with hnRNP complexes, have previously been shown to bind. The present work demonstrates that both of these molecules contribute to CT element-activated transcription in vitro. The pyrimidine-rich strand of the CT element both bound to hnRNP K and competitively inhibited transcription in vitro, suggesting a role for hnRNP K in activating transcription through this single-stranded sequence. Direct addition of recombinant hnRNP K to reaction mixtures programmed with templates bearing single-stranded CT elements increased specific RNA synthesis. If hnRNP K is a transcription factor, then interactions with the RNA polymerase II transcription apparatus are predicted. Affinity columns charged with recombinant hnRNP K specifically bind a component(s) necessary for transcription activation. The depleted factors were biochemically complemented by a crude TFIID phosphocellulose fraction, indicating that hnRNP K might interact with the TATA-binding protein (TBP)-TBP-associated factor complex. Coimmunoprecipitation of a complex formed in vivo between hnRNP K and epitope-tagged TBP as well as binding in vitro between recombinant proteins demonstrated a protein-protein interaction between TBP and hnRNP K. Furthermore, when the two proteins were overexpressed in vivo, transcription from a CT element-dependent reporter was synergistically activated. These data indicate that hnRNP K binds to a specific cis element, interacts with the RNA polymerase II transcription machinery, and stimulates transcription and thus has all of the properties of a transcription factor.

scholarly journals Additional Determinants within Escherichia coli FNR Activating Region 1 and RNA Polymerase α Subunit Required for Transcription Activation

2005 ◽  
Vol 187 (5) ◽  
pp. 1724-1731 ◽  
Author(s):  
K. Derek Weber ◽  
Owen D. Vincent ◽  
Patricia J. Kiley
Keyword(s):  
Escherichia Coli ◽  
Amino Acid ◽  
Rna Polymerase ◽  
Class Ii ◽  
Site Directed Mutagenesis ◽  
Class I ◽  
Side Chains ◽  
Alanine Scanning Mutagenesis ◽  
Α Subunit

ABSTRACT The global anaerobic regulator FNR is a DNA binding protein that activates transcription of genes required for anaerobic metabolism in Escherichia coli through interactions with RNA polymerase (RNAP). Alanine-scanning mutagenesis of FNR amino acid residues 181 to 193 of FNR was utilized to determine which amino acid side chains are required for transcription of both class II and class I promoters. In vivo assays of FNR function demonstrated that a core of residues (F181, R184, S187, and R189) was required for efficient activation of class II promoters, while at a class I promoter, FF(−61.5), only S187 and R189 were critical for FNR activation. Site-directed mutagenesis of positions 184, 187, and 189 revealed that the positive charge contributes to the function of the side chain at positions 184 and 189 while the serine hydroxyl is critical for the function of position 187. Subsequent analysis of the carboxy-terminal domain of the α subunit (αCTD) of RNAP, using an alanine library in single copy, revealed that in addition to previously characterized side chains (D305, R317, and L318), E286 and E288 contributed to FNR activation of both class II and class I promoters, suggesting that αCTD region 285 to 288 also participates in activation by FNR. In conclusion, this study demonstrates that multiple side chains within region 181 to 192 are required for FNR activation and the surface of αCTD required for FNR activation is more extensive than previously observed.

scholarly journals RNA Polymerase I-Promoted HIS4Expression Yields Uncapped, Polyadenylated mRNA That Is Unstable and Inefficiently Translated in Saccharomyces cerevisiae

1998 ◽  
Vol 18 (2) ◽  
pp. 665-675 ◽  
Author(s):  
Hsiu-Jung Lo ◽  
Han-Kuei Huang ◽  
Thomas F. Donahue
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Steady State ◽  
Rna Polymerase ◽  
Rna Polymerase I ◽  
Mutant Form ◽  
Wild Type ◽  
Pol I ◽  
Chromosome Iii ◽  
Polymerase I

ABSTRACT The HIS4 gene in Saccharomyces cerevisiaewas put under the transcriptional control of RNA polymerase I to determine the in vivo consequences on mRNA processing and gene expression. This gene, referred to as rhis4, was substituted for the normal HIS4 gene on chromosome III. Therhis4 gene transcribes two mRNAs, of which each initiates at the polymerase (pol) I transcription initiation site. One transcript, rhis4s, is similar in size to the wild-typeHIS4 mRNA. Its 3′ end maps to the HIS4 3′ noncoding region, and it is polyadenylated. The second transcript,rhis4l, is bicistronic. It encodes the HIS4coding region and a second open reading frame, YCL184, that is located downstream of the HIS4 gene and is predicted to be transcribed in the same direction as HIS4 on chromosome III. The 3′ end of rhis4l maps to the predicted 3′ end of the YCL184 gene and is also polyadenylated. Based on in vivo labeling experiments, the rhis4 gene appears to be more actively transcribed than the wild-type HIS4 gene despite the near equivalence of the steady-state levels of mRNAs produced from each gene. This finding indicated that rhis4mRNAs are rapidly degraded, presumably due to the lack of a cap structure at the 5′ end of the mRNA. Consistent with this interpretation, a mutant form of XRN1, which encodes a 5′-3′ exonuclease, was identified as an extragenic suppressor that increases the half-life of rhis4 mRNA, leading to a 10-fold increase in steady-state mRNA levels compared to the wild-typeHIS4 mRNA level. This increase is dependent on pol I transcription. Immunoprecipitation by anticap antiserum suggests that the majority of rhis4 mRNA produced is capless. In addition, we quantitated the level of His4 protein in a rhis4 xrn1Δ genetic background. This analysis indicates that capless mRNA is translated at less than 10% of the level of translation of capped HIS4 mRNA. Our data indicate that polyadenylation of mRNA in yeast occurs despite HIS4 being transcribed by RNA polymerase I, and the 5′ cap confers stability to mRNA and affords the ability of mRNA to be translated efficiently in vivo.

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