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PMID: 1319572 Published · ppublish English Journal Article Research Support, Non-U.S. Gov't

A ribosomal RNA gene promoter at the telomere of a mini-chromosome in Trypanosoma brucei.

Nucleic acids research ·Vol. 20 ·No. 11 ·1992-06-11 ·Pages 2725-34

Zomerdijk JC, Kieft R, Borst P

Abstract

The parasitic protozoan Trypanosoma brucei has some hundred mini-chromosomes of 50-150 kb, which mainly consist of telomeric repeats, sub-telomeric repeats and internal 177-bp repeats. Their primary function seems to be to expand the repertoire of non-transcribed sub-telomeric variant surface glycoprotein (VSG) genes. Here we report that two of the smaller mini-chromosomes (55 and 60 kb) contain sequences homologous to the ribosomal RNA gene promoter region. We have targeted by homologous recombination the neomycin phosphotransferase (neo(r)) gene behind the promoter on the 55 kb chromosome and show that this promoter mediates the efficient synthesis of properly trans-spliced and polyadenylated neo mRNA. The resulting high resistance to G418 (a neo analogue) is stable in the absence of drug showing that mitotic segregation of this mini-chromosome is precise. Downstream of the transcription start the wild-type version of the ribosomal promoter is flanked by telomeric repeats. The absence of the sub-telomeric repeats found in other T.brucei chromosome ends suggests that the rDNA-telomeric junction has been formed by de novo addition of telomeric repeats to a broken chromosome end (healing). Our results provide a plausible explanation for the alpha-amanitin-resistant transcription of telomeric repeats in T.brucei reported by Rudenko and Van der Ploeg and they show that trypanosomes can efficiently use RNA polymerase I for the expression of sub-telomeric genes, supporting the notion that the alpha-amanitin-resistant transcription of sub-telomeric VSG genes may also be catalyzed by this enzyme.

MeSH Terms
Animals Base Sequence Chromosomes/ultrastructure Genes Kanamycin Kinase Molecular Sequence Data Oligodeoxyribonucleotides/chemistry Phosphotransferases/genetics Promoter Regions, Genetic RNA, Ribosomal/genetics Repetitive Sequences, Nucleic Acid Restriction Mapping Telomere/ultrastructure Trypanosoma brucei brucei/genetics
Chemicals
Oligodeoxyribonucleotides RNA, Ribosomal Phosphotransferases Kanamycin Kinase
Authors & Affiliations
3 authors, click to expand affiliations / ORCID
Zomerdijk J C
Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam.
Kieft R
Borst P
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Article Info
Journal
Nucleic acids research
Abbr.
Nucleic Acids Res
ISSN
0305-1048
DOI
10.1093/nar/20.11.2725
Published
1992-06-11
Pages
2725-34
Language
English
Region
England
NLM ID
0411011
PMCID
PMC336914
Subset
IM
External Links
PubMed source DOI: 10.1093/nar/20.11.2725 PMC Full Text View journal details
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