This paper examines telomeres from an evolutionary perspective. In the monocot plant order Asparagales two evolutionary switch-points in telomere sequence are known. The first occurred when the Arabidopsis-type telomere was replaced by a telomere based on a repeat motif more typical of vertebrates. The replacement is associated with telomerase activity, but the telomerase has low fidelity and this may have implications for the binding of telomeric proteins. At the second evolutionary switch-point, the telomere and its mode of synthesis are replaced by an unknown mechanism. Elsewhere in plants (Sessia, Vestia, Cestrum) and in arthropods, the telomere "typical" of the group is lost. Probably many other groups with "unusual" telomeres will be found. We question whether telomerase is indeed the original end-maintenance system and point to other candidate processes involving t-loops, t-circles, rolling circle replication and recombination. Possible evolutionary outcomes arising from the loss of telomerase activity in alternative lengthening of telomere (ALT) systems are discussed. We propose that elongation of minisatellite repeats using recombination/replication processes initially substitutes for the loss of telomerase function. Then in more established ALT groups, subtelomeric satellite repeats may replace the telomeric minisatellite repeat whilst maintaining the recombination/replication mechanisms for telomere elongation. Thereafter a retrotransposition-based end-maintenance system may become established. The influence of changing sequence motifs on the properties of the telomere cap is discussed. The DNA and protein components of telomeres should be regarded--as with any other chromosome elements--as evolving and co-evolving over time and responding to changes in the genome and to environmental stresses. We describe how telomere dysfunction, resulting in end-to-end chromosome fusions, can have a profound effect on chromosome evolution and perhaps even speciation.

• MeSH
• chromozomy rostlin genetika   metabolismus   MeSH
• fylogeneze MeSH
• genom rostlinný * MeSH
• minisatelitní repetice MeSH
• molekulární evoluce * MeSH
• proteiny vázající telomery fyziologie   MeSH
• repetitivní sekvence nukleových kyselin MeSH
• retroelementy MeSH
• telomery genetika   fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• srovnávací studie MeSH
• Názvy látek
• proteiny vázající telomery MeSH
• retroelementy MeSH

The manner of packing of the terminal DNA loci into nucleosomes and higher order structures may strongly influence their functional interactions. Besides the structural flexibility of telomeric DNA sequences, conserved features of their chromatin including short nucleosome phasing (157 bp) and nucleosome sliding have been described previously. To gain a complementary knowledge of subtelomeres, we have analysed the chromatin structure of two subtelomeric tandem repeats from the plant Silene latifolia: X43.1 and 15Ssp. X43.1 shows two distinct nucleosome periodicities--157 and 188 bp. Preferred positions of its two nucleosomes have been mapped at both low and high resolution and the experimental results correspond to computer-predicted positions. 15Ssp is a newly-discovered sequence showing a telomere-associated position by PCR and a subtelomeric location by pulsed-field gel electrophoresis and fluorescence in situ hybridisation. Its 159 bp sequence unit shows a tandem arrangement and the presence of micrococcal nuclease-hypersensitive sites when either naked DNA or chromatin is digested. Use of a chemical nuclease results in a regular nucleosome ladder of 157 bp periodicity. Moreover, 15Ssp mononucleosomes show instability and absence of specific positioning, features typical for telomeric chromatin.

• MeSH
• DNA rostlinná chemie   genetika   metabolismus   MeSH
• genetické matrice MeSH
• heterochromatin chemie   genetika   metabolismus   MeSH
• hybridizace in situ fluorescenční MeSH
• konformace nukleové kyseliny * MeSH
• Magnoliopsida genetika   MeSH
• mikrokoková nukleasa metabolismus   MeSH
• molekulární sekvence - údaje MeSH
• nukleozomy chemie   genetika   metabolismus   MeSH
• restrikční mapování MeSH
• sekvence nukleotidů MeSH
• sekvenční analýza DNA MeSH
• Southernův blotting MeSH
• tandemové repetitivní sekvence genetika   MeSH
• telomery genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA rostlinná MeSH
• heterochromatin MeSH
• mikrokoková nukleasa MeSH
• nukleozomy MeSH

A single-strand-specific chemical probe, potassium permanganate (KMnO4), was used to study the sequence-dependent conformation periodicity of tandem multicopy repetitive DNA sequences HRS60 and GRS (Nicotiana Species) at the level of single base pair and dinucleotide step. Local DNA structures, sensitive to KMnO4, revealed periodicity of 182 +/- 2 bp, equal to the length of repeat units. Permanganate-sensitive local structures were mapped to both DNA strands of genomic HRS60 sequences and were found to be linked to d(A)n tracts. These adenine tracts are located in the proximity of the intrinsically curved domains. Distamycin A increased reactivity of the DNA but decreased the specificity of DNA cleavage. Similar conformation periodicity has been detected also in the 'canrep' family of repeats (Brassica species). All studied repetitive sequences are predominantly located in the constitutive heterochromatin. We discuss the role of conformation periodicities in relation to a structural code for nucleosome phasing at tandem arrays of DNA repeats.

• MeSH
• Brassica genetika   MeSH
• distamyciny MeSH
• DNA primery genetika   MeSH
• DNA rostlinná chemie   genetika   MeSH
• jedovaté rostliny MeSH
• konformace nukleové kyseliny * MeSH
• manganistan draselný MeSH
• mapování chromozomů MeSH
• molekulární sekvence - údaje MeSH
• molekulární sondy MeSH
• polymorfismus genetický MeSH
• repetitivní sekvence nukleových kyselin * MeSH
• sekvence nukleotidů MeSH
• tabák genetika   MeSH
• vazebná místa MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• distamyciny MeSH
• DNA primery MeSH
• DNA rostlinná MeSH
• manganistan draselný MeSH
• molekulární sondy MeSH
• stallimycin MeSH Prohlížeč