Telomere DNA Protects Chromosomes

In the early stages of her research career, Blackburn mapped out DNA sequences. When studying the chromosomes of Tetrahymena; a unicellular ciliate organism, she identified a DNA sequence that was repeated several times at the ends of the chromosomes. The function of this sequence, CCCCAA, was unclear. At the same time, Szostak had made the observation that a linear DNA molecule; a type of mini-chromosome, was rapidly degraded when introduced into yeast cells.
The DNA end‐sequence of linear DNA molecules from Tetrahymena added to artificial mini chromosomes allowing their long‐term stable maintenance in yeast.

Blackburn presented her results at a conference in 1980. They caught Szostak’s interest and Blackburn and Szostak decided to perform an experiment that would cross the boundaries between very distant species.

From the DNA of Tetrahymena, Blackburn isolated the CCCCAA sequence. Szostak coupled the sequence into the mini-chromosomes and put them back into yeast cells. The results, published in 1982, were striking – the telomere DNA sequence protected the mini-chromosomes from degradation.

As telomere DNA from one organism; Tetrahymena, protected chromosomes in an entirely different one; yeast. This established the existence of a previously unrecognised fundamental mechanism. Later on, it became evident that telomere DNA, with its characteristic sequence, is present in most plants and animals, from amoeba cells to human beings.

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Branka Duric

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