title: Dynamics of telomere length variation in Tetrahymena thermophila.
abstract: We have analyzed the mechanism and dynamics of telomere length variation in the macronucleus of Tetrahymena thermophila. In a newly differentiated macronucleus, the average length of the telomeric repeated sequence, (C4A2 X T2G4)n, is closely regulated. In contrast, in vegetatively dividing cells in log phase, all macronuclear telomeric sequences lengthen coordinately by 3-10 bp per generation until up to 1000 bp are added. In both elongated and short telomeres, characteristic single-stranded breaks on both strands are distally located. Reduction of elongated telomeres to their original length involves either the appearance of a novel type of variant cell, incapable of net telomere elongation, or, under stationary phase conditions, a reversible removal of telomeric sequences. The demonstration that telomeres are dynamic structures provides evidence for a model of telomere length regulation by activities that add and remove telomeric repeats.
mesh_terms: D000818:Animals; D001483:Base Sequence; D002875:Chromosomes; D004261:DNA Replication; D004275:DNA, Ribosomal / Q000378:metabolism; D014644:Genetic Variation; D008957:Models, Genetic; D013768:Tetrahymena / Q000235:genetics*
chemical_list: D004275:DNA, Ribosomal