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T De Lange

Publications and source records attributed to T De Lange.

12 recordsLinked to original sources
PubMed1986

Rapid change of the repertoire of variant surface glycoprotein genes in trypanosomes by gene duplication and deletion.

To study the evolution of the variant surface glycoprotein (VSG) repertoire of trypanosomes we have analysed the DNA region surrounding the VSG 118 gene in different trypanosome strains. We find a remarkable degree of variation in this area. Downstream from the 118 gene a 5.7 X 10(3) base-pair DNA segment containing a potential VSG gene has been quadruplicated in strain 427 of Trypanosoma brucei, but not in most other strains analysed. The VSG 1.1000 gene, located immediately upstream from the 118 gene in one trypanosome strain, has been cleanly deleted in another. Our results are most easily explained by multiple unequal cross-overs between sister chromatids and are the first indication that sister chromatid exchange occurs in trypanosomes.

Animals↗
PubMed1985

Transcription of a transposed trypanosome surface antigen gene starts upstream of the transposed segment.

The non-telomeric variant surface glycoprotein (VSG) genes in Trypanosoma brucei are activated by a duplicative transposition to a telomeric expression site. We have determined the 5' end of the transposed segment of the gene for VSG 117 and infer from comparison with similar data obtained by others that the crossover can occur at variable positions within short repeats present upstream of this gene and in the expression site. We have analysed nascent and steady state transcripts of the transposed gene and its neighbouring expression site DNA. The results indicate that transcription starts upstream of the transposed gene segment in the expression site and that transcripts are rapidly processed at specific points identified by protection of DNA-RNA hybrids against digestion by nuclease S1 or Exo VII. Hence, this gene appears to be activated by a process akin to promoter addition.

Animals↗
PubMed1984

Comparison of the genes coding for the common 5' terminal sequence of messenger RNAs in three trypanosome species.

Messenger RNAs of Trypanosoma brucei share a common 5' terminal sequence of 35 nucleotides, encoded by a mini-exon located in 1.35-kb tandemly linked repeats. We show here that sequences, almost identical to the mini-exon of T. brucei, are present in mRNAs from members of two other kinetoplastid subgenera: Trypanosoma vivax and Trypanosoma cruzi. As in T. brucei, these mini-exons are encoded by small tandemly linked repeat elements. We have determined and compared the nucleotide sequences of the mini-exon repeats from T. brucei, T. vivax and T. cruzi. This analysis shows that the mini-exon, its immediate flanking sequences and a T-rich stretch downstream are conserved, but little else. Our data establish the generality of the novel transcription system, that was first found in T. brucei and that yields mRNAs with common, repeat-encoded, 5' termini.

Animals↗
PubMed1984

Many trypanosome messenger RNAs share a common 5' terminal sequence.

The mRNAs for different variant surface antigens of Trypanosoma brucei start with the same 35 nucleotides. This sequence is encoded by a separate mini-exon, located in a 1.35-kb repetitive element. We have reported that trypanosomes contain many transcripts that hybridize to mini-exon probes, even if they do not make the surface antigens. We show here that these transcripts have the mini-exon sequence at their 5' end; they do not contain other sequences from the mini-exon repeat element and are polyadenylated. We have cloned DNA complementary to trypanosome mRNAs and randomly selected 17 clones containing mini-exon sequences. Thirteen of these are derived from different genes that do not code for surface antigens. We conclude that the mini-exon sequence is a common element at the 5' end of many trypanosome mRNAs. As the 200 genes for mini-exons are highly clustered, linkage of the mini-exon sequence to the remainder of most mRNAs may require discontinuous transcription.

Amino Acid Sequence↗
PubMed1984

Discontinuous synthesis of mRNA in trypanosomes.

Many trypanosome mRNAs have the same sequence of 35 nucleotides at their 5' end, encoded by a mini-exon located in 1.35-kb tandemly linked repeats. We have analysed nascent and steady-state mini-exon transcripts to determine how the mini-exon sequence is joined to the main part of trypanosome mRNAs. We show here that steady-state RNA from Trypanosoma brucei contains a transcript of 141 nucleotides that starts at the 5' border of the mini-exon. Isolated nuclei transcribe the segment corresponding to the 141 nucleotide RNA at a high rate; transcription of other areas of the 1.35-kb mini-exon repeat is approximately 750-fold lower. We propose that transcription of protein-coding genes in trypanosomes is discontinuous and involves the 141-nucleotide transcript as an intermediate.

Animals↗
PubMed1984

Two modes of activation of a single surface antigen gene of Trypanosoma brucei.

Several genes for variant antigens in trypanosomes are activated by duplicative translocation to a telomeric expression site. A second--nonduplicative--mode of activation is restricted to telomeric antigen genes. We show here that the single telomeric gene for antigen 221 can be activated in both ways. We also show that gene 221 is split and that the 5' 35 nucleotide sequence, common to all surface antigen mRNAs, is not encoded within 8.5 kb upstream of the 221 coding region. No major rearrangements are observed within 55 kb upstream of the 221 coding region upon nonduplicative activation. Gene inactivation is usually accompanied by deletion of the gene and at least 8.5 kb upstream and may involve conversion by another telomere. These results are not readily explained by a single expression site model. The duplicative gene 221 activation differs from conventional duplicative activation in the extent of the transposed segment, which is larger and may include the entire segment between gene and telomere.

Animals↗
PubMed1983

Telomere conversion in trypanosomes.

Activation of the gene coding for variant surface glycoprotein (VSG) 118 in Trypanosoma brucei proceeds via a duplicative transposition to a telomeric expression site. The resulting active expression-linked extra copy (ELC) is usually flanked by DNA that lacks sites for most restriction enzymes and that is thought to interfere with the cloning of the ELC as recombinant DNA in Escherichia coli. We have circumvented this problem by cloning an aberrant 118 ELC gene, flanked at the 3'-side by at least 1 kb DNA, that contains restriction enzyme sites. Our analysis shows that this DNA and the 3'-end of the 118 ELC gene are derived from another VSG gene (1.1006) that is permanently located at a telomeric position. We propose that the 3'-end of the 1.1006 gene and (all of) its 3' flanking sequence moved to the expression site by a telomere conversion. Such a telomere conversion can also account for the appearance of an extra copy of the 1.1006 gene detected in a sub-population of our trypanosome strain.

Amino Acid Sequence↗
PubMed1983

Tandem repetition of the 5' mini-exon of variant surface glycoprotein genes: a multiple promoter for VSG gene transcription?

Activation of some variant surface glycoprotein (VSG) genes involves a duplicative transposition to an expression site, which completes the gene by addition of a mini-exon coding for the 5' 35 nucleotides of VSG mRNAs. Using a 22 nucleotide probe we have found some 200 copies of the mini-exon on a tandemly arranged 1.35 kb repetitive element. This repeat is highly conserved in three trypanosome species. The mini-exon on the repeat is flanked by a 5' splice site that resembles the consensus sequence. We have not found a single mini-exon within 10 kb of the transposed VSG gene exon in the expression site. We propose a model in which the arrays of mini-exon repeats function as a repetitive promoter for efficient transcription of VSG genes.

Animals↗
PubMed1982

An analysis of cosmid clones of nuclear DNA from Trypanosoma brucei shows that the genes for variant surface glycoproteins are clustered in the genome.

Trypanosoma brucei contains more than a hundred genes coding for the different variant surface glycoproteins (VSGs). Activation of some of these genes involves the duplication of the gene (the basic copy or BC) and transposition of the duplicate to an expression site (yielding the expression-linked copy or ELC). We have cloned large fragments of genomic DNA in cosmid vectors in Escherichia coli. Cosmids containing the BCs of genes 117, 118 and 121 were readily obtained, but DNA containing the ELCs was strongly selected against in the cosmid and plasmid cloning systems used. We have analysed the distribution of VSG genes in the genome using probes for the sequences at the edges of the transposed segment which are partially homologous among these genes. In genomic cosmid clone banks, about 9% of all colonies hybridize with probes from the 5'- and 3'-edges of the transposed segment, showing that these sequences are linked in the genome. Moreover, the 117 and 118 BC cosmids contain several additional putative VSG genes in tandem, as deduced from hybridization and sequence analyses. We conclude that the VSG genes are highly clustered and share common sequences at the borders of the transposed segment.

Animals↗
PubMed1982

RNA splicing is required to make the messenger RNA for a variant surface antigen in trypanosomes.

The expression of the gene for variant surface glycoprotein (VSG) 118 in Trypanosoma brucei is activated by transposing a DNA segment containing the gene and 1-2 kb in front of it to an expression site elsewhere in the genome. By S1 nuclease protection and RNA blotting experiments we show here the presence of several minor transcripts in trypanosomes synthesizing VSG 118, one of which covers the entire transposed segment. Comparison of the sequence of the 5' terminal segment of VSG 118 messenger RNA (mRNA), determined by primed reverse transcription, and the corresponding region of the 118 VSG gene, shows that the 5' terminal 34 nucleotides of the mRNA are not encoded in the 118 VSG gene contiguous with the remainder of the mRNA. We conclude that synthesis of a VSG mRNA involves splicing of a much longer primary transcript, which may start outside the transposed segment.

Animals↗