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5 Saccharomyces Telomeres: Function, Structure, and Replication

Virginia A. Zakian


The concept of the telomere as an essential part of the eukaryotic chromosome stems from the pioneering work carried out in the 1930s by Herman Muller and Barbara McClintock (see Gall, this volume). Muller X-irradiated male Drosophila and analyzed the chromosomal rearrangements that resulted. Although he recovered many rearrangements, he did not recover terminal deletions (i.e., chromosomes lacking an end). He reasoned that the end of the chromosome must be a special structure, the telomere, that is essential for the stable maintenance of linear chromosomes, hence the failure to obtain chromosomes without an end (Muller 1938). McClintock extended these observations by studying the fate of broken chromosomes in corn. She found that broken ends, unlike natural ends, fuse with other broken ends, thereby creating a dicentric chromosome which would often break in a subsequent mitosis. Thus, McClintock’s work suggested that one essential function of telomeres is to prevent chromosomes from fusing with one another (McClintock 1939McClintock 1941; Gall, this volume). The studies of Muller and McClintock were carried out before DNA was known to be the genetic material. With the advent of DNA sequencing, it became clear that the very ends of chromosomes carry special DNA sequences. As in most organisms, Saccharomyces telomeres consist of multiple copies of a very simple repeated DNA. In wild-type yeast, each end of each chromosome bears about 300 ± 75 bp of C2–3A(CA)1–6/(TG)1–6TG2–3 DNA, commonly abbreviated C1–3A/TG1–3 (see Henderson, this volume, and below).

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