Cancer and the knockout mouse

Article Abstract:

The specialized structures known as telomeres are found at the end of linear chromosomes and normally consist of arrays of a short DNA sequence. The function of the sequence (TTAGGG in vertebrates) is two-fold: firstly to prevent random breaks in natural chromosome ends, and secondly they solve the problem of end-replication. The enzyme telomerase synthesizes TTAGGG repeats. A new study of telomerase-deficient mice seeks to discover whether the absence of telomere-specific DNA sequences activates cell-cycle arrest. Details of the study are presented.

DNA sequencers

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Bumps on the road to immortality

Article Abstract:

Telomeric DNA is needed to preserve the ends of chromosomes and the integrity of the genome. One model proposes that normal cells telomeres shorten at each generational doubling and ultimately erode causing cells to senesce. Kiyono and colleagues have suggested that senescence in certain cell types is difficult to avoid. They have studied keratinocytes and mammary epithelial cells, suggesting that their immortalization requires hTERT gene expression and inactivation of the retinoblastoma (Rb)p16INK4a tumor suppressor pathway.

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Capping off the ends

Article Abstract:

Steve Schultz and colleagues have described the way in which the ciliate Oxytricha nova handles the ends of its chromosomal DNA (telomeres). The crystal structure of the telomere end-binding protein (TEBP) has been solved and shows how it is tailored to the problem. TEBP recognizes any overhang and forms a protective layer over the end of telomeric DNA, binding only to the 3' terminus of single-stranded G(sub4)T(sub4) DNA.

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