DNA, Protozoan

Publication Title: 
Cold Spring Harbor Symposia on Quantitative Biology
Author(s): 
Lee, M. S.
Gallagher, R. C.
Bradley, J.
Blackburn, E. H.
Publication Title: 
Proceedings of the National Academy of Sciences of the United States of America

Macronuclear telomeres in Oxytricha exist as DNA-protein complexes in which the termini of the G-rich strands are bound by a 97-kDa telomere protein. During telomeric DNA replication, the replication machinery must have access to the G-rich strand. However, given the stability of telomere protein binding, it has been unclear how this is accomplished. In this study we investigated the ability of several different DNA polymerases to access telomeric DNA in Oxytricha telomere protein-DNA complexes.

Author(s): 
Shippen, D. E.
Blackburn, E. H.
Price, C. M.
Publication Title: 
The Journal of Eukaryotic Microbiology

Site-directed mutagenesis of the telomerase RNA from Tetrahymena thermophila was used previously to demonstrate the templating function of a sequence within this RNA; this sequence specifies the sequence of telomeric DNA in vivo. The possible functional importance of a phylogenetically conserved nucleotide outside the telomerase RNA template region was investigated by a similar experimental approach.

Author(s): 
Romero, D. P.
Blackburn, E. H.
Publication Title: 
Annual Review of Biochemistry
Author(s): 
Blackburn, E. H.
Publication Title: 
Genes & Development

The ciliated protozoan Tetrahymena thermophila contains two nuclei that differ dramatically in function, chromosome size and number, chromatin structure, and mode of division. It is possible that the telomeres of the two nuclei have different functions. Although macronuclear telomeric DNA has been well characterized and consists of tandem G4T2/C4A2 repeats that are synthesized by the enzyme telomerase, micronuclear telomeres have not been isolated previously.

Author(s): 
Kirk, K. E.
Blackburn, E. H.
Publication Title: 
Proceedings of the National Academy of Sciences of the United States of America

Paramecium tetraurelia cells have a limited clonal life span and die after approximately 200 fissions if they do not undergo the process of autogamy or conjugation. To test the possibility that cellular senescence of this species is caused by telomere shortening, we analyzed the genomic DNA of the macronucleus during the clonal life span of P. tetraurelia. We found that telomeric DNA sequences were not shortened during the interval of decreased fission rate and cellular death, defined as senescence in these cells.

Author(s): 
Gilley, D.
Blackburn, E. H.
Publication Title: 
Molecular and Cellular Biology

The ribonucleoprotein enzyme telomerase is a specialized reverse transcriptase that synthesizes telomeric DNA by copying a template sequence within the telomerase RNA. Here we analyze the actions of telomerase from Tetrahymena thermophila assembled in vivo with mutated or wild-type telomerase RNA to define further the roles of particular telomerase RNA residues involved in essential enzymatic functions: templating, substrate alignment, and promotion of polymerization.

Author(s): 
Gilley, D.
Blackburn, E. H.
Publication Title: 
Journal of Molecular Biology

The telomeric d(GGGGTT).d(AACCCC) repeat tracts (G4T2 repeats) in Tetrahymena thermophila macronuclei were shown previously to be packaged in a non-nucleosomal DNA-protein complex. Here, we demonstrate that these telomeric repeats, together with a short region of the immediately adjacent non-telomeric sequence, exist in two distinct types of chromatin.

Author(s): 
Cohen, P.
Blackburn, E. H.
Publication Title: 
Cell

Healing of a broken chromosome and in eukaryotes involves acquisition of a telomere. During macronuclear development in ciliated protozoans, germline chromosomes are fragmented into linear subchromosomes, whose ends are healed by de novo addition of telomeres. We showed previously that the ribonucleoprotein enzyme telomerase elongates preexisting telomeres by synthesizing one telomeric DNA strand, using a template sequence in the RNA moiety of the enzyme.

Author(s): 
Yu, G. L.
Blackburn, E. H.
Publication Title: 
Science (New York, N.Y.)

Telomeres are essential for chromosome stability, but their functions at specific cell-cycle stages are unknown. Telomeres are now shown to have a role in chromosome separation during mitosis. In telomeric DNA mutants of Tetrahymena thermophila, created by expression of a telomerase RNA with an altered template sequence, division of the germline nucleus was severely delayed or blocked in anaphase. The mutant chromatids failed to separate completely at the midzone, becoming stretched to up to twice their normal length. These results suggest a physical block in mutant telomere separation.

Author(s): 
Kirk, K. E.
Harmon, B. P.
Reichardt, I. K.
Sedat, J. W.
Blackburn, E. H.

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