Regulation of telomere length and function by a Myb-domain protein in fission yeast

Telomeres, the specialized nucleoprotein structures that comprise the ends of eukaryotic chromosomes(1,2), are essential for complete replication(3-5), and regulation of their length has been a focus of research on tumorigenesis(6-8). In the budding yeast Saccharomyces cerevisiae, the protein Rap1p binds to telomeric DNA and functions in the regulation of telomere length(9-12). A human telomere protein, hTRF (human TTAGGG repeat factor) binds the telomere sequence in vitro(13) and localizes to telomeres cytologically(14), but its functions are not yet known. Here we use a genetic screen to identify a telomere protein in fission yeast, Taz1p (telomere-associated in Schizosaccharomycesrces pombe), that shares homology to the Myb proto-oncogene DNA-binding domain with hTRF. Disruption or deletion of the taz1(+) gene causes a massive increase in telomere length. Taz1p is required for the repression of telomere-adjacent gene expression and for normal meiosis or sporulation. It may be a negative regulator of the telomere-replicating enzyme, telomerase(1,3), or may protect against activation of telomerase-independent pathways of telomere elongation(8).