Sequence-specific binding of Taz1p dimers to fission yeast telomeric DNA

The fission yeast (Schizosaccharomyces pombe) taz1 gene encodes a telomere- associated protein, It contains a single copy of a Myb-like motif termed th e telobox that is also found in the human telomere binding proteins TRF1 an d TRF2, and Tbf1p, a protein that binds to sequences found within the subte lomeric regions of budding yeast (Saccharomyces cerevisiae) chromosomes, Ta z1p was synthesised in vitro and shown to bind to a fission yeast telomeric DNA fragment in a sequence specific manner that required the telobox motif . Like the mammalian TRF proteins, Taz1p bound to DNA as a preformed homodi mer, The isolated Myb-like domain was also capable of sequence specific DNA binding, although with less specificity than the full-length dimer. Surpri singly, a protein extract produced from a taz1-fission yeast strain still c ontained the major telomere binding activity (complex I) we have characteri sed previously, suggesting that there could be other abundant telomere bind ing proteins in fission yeast. One candidate, SpX, was also synthesised in vitro, but despite the presence of two telobox domains, no sequence specifi c binding to telomeric DNA was detected.