TDP1 is an HMG chromatin protein facilitating RNA polymerase I transcription in African trypanosomes

The African trypanosomes express two major surface proteins, the variant surface glycoprotein (VSG) and the procyclic acidic repetitive protein (PARP). The RNA polymerase that transcribes the VSG and PARP genes shares many characteristics with RNA polymerase I. We show that although there is very little similarity in nucleotide sequence, the functional structure of a trypanosome rRNA promoter is almost identical to that of the PARP promoter. Further, domains from the PARP promoter can functionally substitute for the corresponding parts of the rRNA promoter, and vice versa.

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The PARP and rRNA promoters of Trypanosoma brucei are composed of dissimilar sequence elements that are functionally interchangeable.

Molecular and Cellular Biology ◽

10.1128/mcb.14.9.5804 ◽

1994 ◽

Vol 14 (9) ◽

pp. 5804-5811 ◽

Cited By ~ 43

Author(s):

L Janz ◽

C Clayton

Keyword(s):

Rna Polymerase ◽

Rna Polymerase I ◽

Surface Proteins ◽

Surface Glycoprotein ◽

African Trypanosomes ◽

Sequence Elements ◽

Major Surface Proteins ◽

Major Surface ◽

Polymerase I ◽

Repetitive Protein

The African trypanosomes express two major surface proteins, the variant surface glycoprotein (VSG) and the procyclic acidic repetitive protein (PARP). The RNA polymerase that transcribes the VSG and PARP genes shares many characteristics with RNA polymerase I. We show that although there is very little similarity in nucleotide sequence, the functional structure of a trypanosome rRNA promoter is almost identical to that of the PARP promoter. Further, domains from the PARP promoter can functionally substitute for the corresponding parts of the rRNA promoter, and vice versa.

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The Trypanosomatid-Specific N Terminus of RPA2 Is Required for RNA Polymerase I Assembly, Localization, and Function

Eukaryotic Cell ◽

10.1128/ec.00036-12 ◽

2012 ◽

Vol 11 (5) ◽

pp. 662-672 ◽

Cited By ~ 8

Author(s):

Jan-Peter Daniels ◽

Keith Gull ◽

Bill Wickstead

Keyword(s):

Rna Polymerase ◽

Nuclear Localization ◽

Rna Polymerase I ◽

Growth Defect ◽

Protein Coding ◽

African Trypanosomes ◽

Protein Coding Genes ◽

Pol I ◽

N Terminus ◽

Polymerase I

ABSTRACT African trypanosomes are the only organisms known to use RNA polymerase I (pol I) to transcribe protein-coding genes. These genes include VSG , which is essential for immune evasion and is transcribed from an extranucleolar expression site body (ESB). Several trypanosome pol I subunits vary compared to their homologues elsewhere, and the question arises as to how these variations relate to pol I function. A clear example is the N-terminal extension found on the second-largest subunit of pol I, RPA2. Here, we identify an essential role for this region. RPA2 truncation leads to nuclear exclusion and a growth defect which phenocopies single-allele knockout. The N terminus is not a general nuclear localization signal (NLS), however, and it fails to accumulate unrelated proteins in the nucleus. An ectopic NLS is sufficient to reinstate nuclear localization of truncated RPA2, but it does not restore function. Moreover, NLS-tagged, truncated RPA2 has a different subnuclear distribution to full-length protein and is unable to build stable pol I complexes. We conclude that the RPA2 N-terminal extension does not have a role exclusive to the expression of protein-coding genes, but it is essential for all pol I functions in trypanosomes because it directs trypanosomatid-specific interactions with RPA1.

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

Eukaryotic Cell ◽

10.1128/ec.00282-09 ◽

2009 ◽

Vol 9 (1) ◽

pp. 148-154 ◽

Cited By ~ 64

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.

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