Developmentally regulated telomere addition in<i>Tetrahymena thermophila</i>

Spangler, Elizabeth; Ryan, Thecla; Blackburn, Elizabeth H.

doi:10.1093/nar/16.12.5569

Cited by 25 publications

(16 citation statements)

References 38 publications

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“…First, the healed end indicates that the Ca7 repeats are sufficient to function as a C. albicans telomere in the absence of the repetitive subtelomeric sequences that are present on native C. albicans telomeres. Evidence from telomere formation in ciliates and from other healed ends indicates that the terminal repeats of other species are also sufficient to function as telomeres (2,6,8,29,39,42,44). The second important implication of the C. albicans healed end is that it suggests that C. albicans cells have a mechanism for the de novo addition of telomere sequences to a free DNA end.…”

Section: Resultsmentioning

confidence: 99%

Unusually large telomeric repeats in the yeast Candida albicans.

McEachern¹,

Hicks²

1993

Mol. Cell. Biol.

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We have identified sequences at the telomeres of the yeast Candida albicans and have found that they are composed of tandem copies of a 23-bp sequence. Through the cloning of native telomeric ends and the characterization and cloning of a "healed" end, we demonstrate that these repeated sequences are sufficient to function as a telomere. All copies of the 23-bp repeat that have been sequenced from a number of C. albicans strains are identical. In contrast, adjacent subtelomeric sequences are variable both between strains and within the WO-1 strain. In the WO-1 strain, the lengths of the telomeres are dependent upon growth temperature and are substantially longer at higher temperatures. Telomere growth is accompanied by increases in the number of the 23-bp repeats present on the telomeric fagments. These results suggest that either telomerasemaintained telomeres can be more complex in structure than was previously imagined or that Candida telomeres are maintained via a telomerase-independent mechanism.Telomeres are the specialized structures at the ends of eukaryotic chromosomes (for recent reviews, see references 5 and 47). They serve as a cap on chromosome termini, preventing end-to-end fusion and exonucleolytic degradation and allowing the complete replication of chromosomes. Telomeric DNA from diverse organisms has been shown previously to share many structural features. Those so far described consist entirely of tandemly repeated sequences, from 5 to 9 bp in length, generally with a G-rich strand that is oriented 5' to 3' toward the end of the chromosome. Telomeres from a number of organisms have 3' overhanging tails that are capable of forming unusual non-Watson-Crick base-paired structures (14,15,18).A ribonucleoprotein enzyme activity that synthesizes telomeric repeats on the ends of DNA molecules, termed telomerase, has been identified in the ciliate genera Tetrahymena, Oxytricha, and Euplotes and in human cell extracts, (9,24,37,46). The RNA component of this enzyme has been identified in Tetrahymena and Euplotes spp. In each case it carries within it a sequence that is complementary to the telomere repeat and functions as the template for the synthesis of telomeric repeats (10,37,45). Telomerase thus appears to be a specialized reverse transcriptase.We previously identified a middle repetitive sequence from the asexual yeast Candida albicans that is present on all chromosomes of each of the strains that we have examined (34). This sequence, designated Ca7, is composed of a tandem series of 23-bp repeats and was shown by Bal 31 exonuclease digestion to reside very near to the ends of C. albicans chromosomes (34). In this work we demonstrate that the Ca7 repeats are present on a healed chromosomal end and that they are present at the termini of all cloned copies of DNA fragments which contain them. Additionally, we show that the number of telomeric Ca7 repeats changes when cells are grown at different temperatures. MATERIALS AND METHODSStrains and growth conditions. C. albicans WO-1 has been described e...

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Section: Resultsmentioning

confidence: 99%

Unusually large telomeric repeats in the yeast Candida albicans.

McEachern¹,

Hicks²

1993

Mol. Cell. Biol.

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“…This idea is appealing because in vivo data point to a need for telomerase to bind to a specific DNA sequence to act. In Tetrahymena, sequences derived from the sites of telomere addition in macronuclear DNA do not contain C4A2 repeats, and they are not utilized by telomerase in vitro (Spangler et al 1988). This result suggests that there may be other telomerase recognition sequences proximal to the sites of telomere addition in Tetiahymena macronuclear chromosomes.…”

Section: Discussionmentioning

confidence: 99%

A yeast protein that binds to vertebrate telomeres and conserved yeast telomeric junctions.

Liu¹,

Tye²

1991

Genes Dev.

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“…Clues to some of these complex mechanisms have been obtained: in Tetrahymena, Yao et al (1990) identified chromosome breakage sequences involved in the fragmentation process. Other studies in Tetrahymena (Spangler et al, 1988;Yu and Blackburn, 1991) and also in Oxytricha (Zahler and Prescott, 1988) and Paramecium (Baroin et al, 1987;Bourgain and Katinka, 1991) are contributing to the understanding of telomerization. Finally, studies in hypotrichous ciliates have revealed the existence of 'DNA splicing', which consists in the specific elimination of short intragenic sequences (IES) during the differentiation of micro into macronuclear chromosomes (Klobutcher et al, 1984).…”

Section: Introductionmentioning

confidence: 99%

The beta-tubulin genes of Paramecium are interrupted by two 27 bp introns.

Dupuis

1992

The EMBO Journal

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In the ciliate Paramecium tetraurelia, the analysis of the tubulin gene family has revealed the existence of four a and three 3 genes. We show here that the coding sequence of the first (3-tubulin gene to be cloned and sequenced is interrupted by two short non-coding sequences of 27 bp each, which present at their extremities the pairs GT/AG, characteristic of eukaryotic pre-mRNA introns, and the internal pentanucleotide TTAAT, consensual inTetrahymena introns. We demonstrate by PCR experiments that the three macronuclear ,B-tubulin genes contain these sequences in similar positions, thereby ruling out the possibility that these sequences are ciliate IES present in the micronucleus and eliminated in the transcriptionally active macronucleus. Si mapping analysis and mRNA sequencing show that the sequences are absent from the j-tubulin transcripts. These sequences are the first introns described in protein encoding genes in P.tetraurelia and the shortest known introns altogether.

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Developmentally regulated telomere addition inTetrahymena thermophila

Cited by 25 publications

References 38 publications

Unusually large telomeric repeats in the yeast Candida albicans.

Unusually large telomeric repeats in the yeast Candida albicans.

A yeast protein that binds to vertebrate telomeres and conserved yeast telomeric junctions.

The beta-tubulin genes of Paramecium are interrupted by two 27 bp introns.

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