Modulation of Telomere Length Dynamics by the Subtelomeric Region of Tetrahymena Telomeres

Naduparambil K. Jacob, Angela R. Stout, and Carolyn M. Price*

Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524

Monitoring Editor: Joseph Gall

Tetrahymena telomeres usuallyconsist of $~$ 250 base pairs of T₂G₄repeats, but they can growto reach a new length set point of up to 900 base pairs whenkept in log culture at 30°C. We have examined the growthprofile of individual macronuclear telomeres and have foundthat the rate and extent of telomere growth is affected by thesubtelomeric region. When the sequence of the rDNA subtelomericregion was altered, we observed a decrease in telomere growthregardless of whether the GC content was increased or decreased.In both cases, the ordered structure of the subtelomeric chromatinwas disrupted, but the effect on the telomeric complex was relativelyminor. Examination of the telomeres from non-rDNA chromosomesshowed that each telomere exhibited a unique and characteristicgrowth profile. The subtelomeric regions from individual chromosomeends did not share common sequence elements and they each hada different chromatin structure. Thus, telomere growth is likelyto be regulated by the organization of the subtelomeric chromatinrather than by a specific DNA element. Our findings suggestthat at each telomere the telomeric complex and subtelomericchromatin cooperate to form a unique higher order chromatinstructure that controls telomere length.

^*Corresponding author.

Carolyn M. Price, E-mail: Carolyn.Price{at}uc.edu