DEFECTIVE MEIOSIS IN TELOMERE-SILENCING MUTANTS OF SCHIZOSACCHAROMYCES-POMBE

During meiotic prophase, chromosomes frequently adopt a bouquet-like a rrangement, with their telomeres clustered close to the nuclear periph ery(1-3). A dramatic example of this occurs in the fission yeast, Schi zosaccharomyces pombe, where all telomeres aggregate adjacent to the s pindle pole body (SPB)(4-7). Nuclei then undergo rapid traverses of th e cell, known as 'horsetail' movement, which is led by the SPB draggin g telomeres and chromosomes behind(4,6,7). This process may initiate o r facilitate chromosome pairing before recombination and meiosis. With the aim of identifying components involved in telomere structure and function, we report here the isolation of S. pombe mutants defective i n the ability to impose transcriptional silencing on genes placed near telomeres(8). Two of these mutants, lot2-s17 and lot3-uv3, also displ ay a dramatic lengthening of telomeric repeats. lot3-uv3 carries a mut ation in Tazl (ref. 9), a telomere-binding protein containing a Myb-li ke moth similar to two human telomere-binding proteins(10,11). Meiosis is aberrant in these mutant yeast strains, and our analysis demonstra tes a decreased association of telomeres with the SPB in meiotic proph ase, This results in defective 'horsetail' movement, a significant red uction in recombination, low spore viability and chromosome missegrega tion through meiosis.