Taz1p and Teb1p, two telobox proteins in Schizosaccharomyces pombe, recognize different telomere-related DNA sequences

Band shift assays were used to study proteins from the fission yeast that b ind double-stranded telomeric repeat sequences. We also examine general DNA binding properties of the telobox domain, which characterizes telomere-bin ding proteins from a range of species. We demonstrate that Taz1p has a high affinity for the fission yeast telomeric repeat, consistent with genetic r esults implicating this protein in telomere maintenance, A second Schizosac charomyces pombe telobox protein, Teb1p, is shown to bind with high affinit y to the vertebrate repeat and with low affinity to the fission yeast telom eric DNA. When tested on G-rich single-stranded telomeric DNA, all these pr oteins bind with very low affinity, much like the human telomere-binding pr otein TRF1. Recombinant proteins containing just the telobox domains reprod uce the specificity of binding demonstrated for the corresponding full-leng th proteins, indicating that the telobox domain is indeed responsible for s pecific DNA recognition. The presence of possible Teb1p-binding sites upstr eam of many genes suggests a role for this protein as a general transcripti on factor. Finally, band shift experiments with whole cell extracts from wi ld-type and taz1(-) strains suggest that in addition to Taz1p, S.pombe has another major telomere-binding activity.