Trypanosoma brucei: a surface antigen mRNA is discontinuously transcribed from two distinct chromosomes.

Guyaux, Michel; Cornelissen, A. W. C. A.; Pays, Étienne; Steinert, Maurice; Borst, Piet

doi:10.1002/j.1460-2075.1985.tb03729.x

Cited by 54 publications

(22 citation statements)

References 41 publications

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“…1). This transcript starts about 90 base pairs (bp) downstream from the poly(A) addition site of the first gene (ESAG 7) and extends to the poly(A) addition site of the second gene (ESAG 6 observed here appeared to be the first possible ones downstream from the polyadenylation region of ESAG 7 mRNA (Table 1). Thus, the 2.3-kb transcripts are about 0.7 kb larger than the mature ESAG 6 mRNA because of splicing at unusual locations far upstream from ESAG 6 but as close as possible to the end of the ESAG 7 mRNA.…”

Section: Methodsmentioning

confidence: 80%

“…This conclusion is also in agreement with our observation that the effect of UV irradiation cannot be mimicked by heat shock (E. Pays and H. Coquelet, unpublished data), as heat shock is known to inhibit splicing (14,28 is spliced, any RNA sequence immediately upstream from the 3' splice site would be degraded as a branched intermediate. The substrate for this splicing could be a 2.4-kb transcript starting at the cleavage site for polyadenylation of ESAG 7 and ending at the polyadenylation site of ESAG 6 (Fig. 3).…”

Section: Methodsmentioning

confidence: 99%

“…However, no direct evidence of the existence of polycistronic transcripts has yet been provided. The trypanosome genes appear devoid of introns, but splicing of the RNA precursors occurs; a 39-nucleotide sequence called the miniexon is cleaved from a short precursor and is added at the 5' termini of all mature mRNAs, irrespective of whether these RNAs are transcribed from the same chromosome as the miniexon (7,11,16,24). This splicing appears necessary for RNA translation (4,27).…”

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Trypanosoma brucei: enrichment by UV of intergenic transcripts from the variable surface glycoprotein gene expression site.

Coquelet¹,

Tebabi²,

Pays³

et al. 1989

Mol. Cell. Biol.

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The expression site for the variable surface glycoprotein (VSG) gene AnTat 1.3A of Trypanosoma brucei is 45 kilobases long and encompasses seven expression site-associated genes (ESAGs) (E. Pays, P. Tebabi, A. Pays, H. Coquelet, P. Revelard, D. Salmon, and M. Steinert, Cell 57:835-845, 1989). After UV irradiation, several large transcripts from the putative promoter region were strongly enriched. We report that one such major transcript starts near the poly(A) addition site of the first gene (ESAG 7), spans the intergenic region, and extends to the poly(A) addition site of the second gene (ESAG 6), thus bypassing the normal 3' splice site of the ESAG 6 mRNA. Since this transcript is spliced, we conclude that UV irradiation does not inhibit splicing but stabilizes unstable processing products. This demonstrates that at least some intergenic regions of the VSG gene expression site are continuously transcribed in accordance with a polycistronic transcription model.In African trypanosomes, antigenic variation is achieved by frequent changes of the variable surface glycoprotein (VSG). Different VSG genes can be expressed, but only one is usually transcribed at a time, and different switching mechanisms have been described (for recent reviews, see references 3, 19, and 26). The transcribed VSG gene is located at the end of a telomeric expression site, which also contains other genes (expression site-associated genes [ESAGs]) and is repeated in 5 to 20 slightly different versions in the genome. This transcription exhibits several characteristics: (i) it resists inhibition by oa-amanitin; (ii) it is preferentially stopped by a lowering of temperature; and (iii) it seems to start upstream from the ESAGs, so that several genes may belong to the same transcription unit (1, 10, 19a, 23). The latter characteristic has also been reported for other genes, such as tubulin, calmodulin, and actin genes and genes of the glycolytic pathway, suggesting that in Trypanosoma brucei, transcription in general might be polycistronic (2,5,8,9,25). However, no direct evidence of the existence of polycistronic transcripts has yet been provided. The trypanosome genes appear devoid of introns, but splicing of the RNA precursors occurs; a 39-nucleotide sequence called the miniexon is cleaved from a short precursor and is added at the 5' termini of all mature mRNAs, irrespective of whether these RNAs are transcribed from the same chromosome as the miniexon (7,11,16,24). This splicing appears necessary for RNA translation (4,27).In an attempt to map the transcription promoter of the AnTat 1.3A VSG gene expression site, we have measured the relative sensitivity of its transcription to inhibition by UV irradiation, as was done for another VSG gene expression site by Johnson et al. (9). As reported previously (19a), we found that transcription of a particular region, located about 45 kilobases (kb) upstream from the VSG gene, appears to be selectively and strongly stimulated by UV light. This apparent stimulation also characterizes the promoter reg...

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Section: Methodsmentioning

confidence: 80%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Trypanosoma brucei: enrichment by UV of intergenic transcripts from the variable surface glycoprotein gene expression site.

Coquelet¹,

Tebabi²,

Pays³

et al. 1989

Mol. Cell. Biol.

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“…Antigenic variation of the VSG coat is brought about by the inactivation of the previously expressed VSG gene and the activation of a new VSG gene (for reviews, see references 8, 22, 46, 48, and 67). The expressed VSG gene is located at one of several telomeric VSG gene expression sites (19,26,71). Antigenic switches can result from the translocation of a new, previously silent or basic-copy (BC) VSG gene into a transcriptionally engaged expression site, generating an expression-linked copy (ELC; 27, 51, 53).…”

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confidence: 99%

“…The maturation of the polycistronic pre-mRNA, generated from transcription of the expression sites, involves the trans-splicing of a capped 39-nucleotide (nt) miniexon donor RNA onto the 5' end of every pre-mRNA (7,11,14,20,21,23,26,30,41,44,45,47,56,61,64,69,70,74). In contrast to the transcription * Corresponding author.…”

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confidence: 99%

Characterization of VSG gene expression site promoters and promoter-associated DNA rearrangement events.

Gottesdiener¹,

Chung²,

Brown³

et al. 1991

Mol. Cell. Biol.

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The expressed variant cell surface glycoprotein (VSG) gene of Trypanosoma brucei is located at the 3' end of a large, telomeric, polycistronic transcription unit or expression site. We show that the region 45 kb upstream of the VSG gene, in the expression site on a 1.5-Mb chromosome, contains at least two promoters that are arranged in tandem, directing the transcription of the expression site. DNA rearrangement events occur specifically, at inactivation of the expression site, and these events delete the most upstream transcribed region and replace it with a large array of simple-sequence DNA, leaving the downstream promoter intact. Because of the placement of simple-sequence DNA, the remaining downstream promoter now becomes structurally identical to previously described VSG promoters. The downstream promoter is repetitive in the genome, since it is present at several different expression sites. Restriction fragment length polymorphism mapping allows grouping of the expression sites into two families, those with and those without an upstream transcription unit, and the DNA rearrangement events convert the expression sites from one type to the other. Deletion of the upstream transcription unit also leads to the loss of several steady-state RNAs. The findings may indicate a role for promoter-associated DNA rearrangement events, and/or interactions between tandemly arranged promoters, in expression site transcriptional control.The African trypanosome Trypanosoma brucei survives in the bloodstream of its mammalian host by periodically changing the antigenic composition of its cell surface coat. This dense homogeneous coat consists of identical proteins, the variant cell surface glycoproteins (VSGs;15,16,73). Antigenic variation of the VSG coat is brought about by the inactivation of the previously expressed VSG gene and the activation of a new VSG gene (for reviews, see references 8, 22, 46, 48, and 67). The expressed VSG gene is located at one of several telomeric VSG gene expression sites (19,26,71). Antigenic switches can result from the translocation of a new, previously silent or basic-copy (BC) VSG gene into a transcriptionally engaged expression site, generating an expression-linked copy (ELC; 27, 51, 53). Alternatively, antigenic switches can occur by the inactivation of one telomeric VSG gene expression site and the transcriptional activation of a new expression site (4,9,13,40,43,69,71). The mechanisms of control of expression sites switches have remained obscure, and it has been assumed that expression sites can be activated in situ, without detectable changes in their DNA sequences (76). Alternative models propose that DNA rearrangements affect transcription or that constitutive activity of expression site promoters is followed by posttranscriptional control (8, 49).The expression sites encode large (up to 60 kb) polycistronic transcription units, with several expression site-associated genes (ESAGs) in addition to the telomerically located VSG gene (1,18,28,31,52,55,62,63). The maturation of the polyc...

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What the papers say: Molecular karyotypes: Separating chromosomes on gels

Corcoran

1985

BioEssays

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SummaryFor many years, there has been a gap in our capacity to study the structure and organization of chromosomal DNA molecules. The very small genomes of some viruses and bacteriophages (d 50,000 bp or 50 kb) are amenable to analysis by conventional gel electrophoresis, while the extremely large DNA molecules (> 100,000 kb) comprising the chromosomes of higher eukaryotes have been analysed under the light microscope, using a range of banding and in situ hybridization techniques. However, intact DNA molecules with sizes between these two extremes have been largely inaccessible experimentally. This gap has recently been bridged with the development of two-dimensional electrophoretic procedures that allow the separation and purification of chromosome-sized DNA molecules ranging from -50 kb to several thousand kb.'-3 There are currently two variations of the technique in use: pulsed field gradient (PFG) gel elec trophoresisl 7 and or thogonal-jieldalteration gel electrophoresis (OFAGE).3 Both are based on a common principle, difering primarily in the geometry of the electrodes. Already, they have been employed to determine the approximate chromosome sizes and numbers for a variety of lower eukaryotes, including yeast and several protozoa.2-10 These ' molecular karyotypes' provide fundamental information about the genomic organization of each organism, and allow very rapid construction of linkage maps. Surprisingly, they have also revealed a remarkable plasticity in the genomes of several lower eukaryotes.

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Trypanosoma brucei: a surface antigen mRNA is discontinuously transcribed from two distinct chromosomes.

Cited by 54 publications

References 41 publications

Trypanosoma brucei: enrichment by UV of intergenic transcripts from the variable surface glycoprotein gene expression site.

Trypanosoma brucei: enrichment by UV of intergenic transcripts from the variable surface glycoprotein gene expression site.

Characterization of VSG gene expression site promoters and promoter-associated DNA rearrangement events.

What the papers say: Molecular karyotypes: Separating chromosomes on gels

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