YEAST TELOMERES EXERT A POSITION EFFECT ON RECOMBINATION BETWEEN INTERNAL TRACTS OF YEAST TELOMERIC DNA

In Saccharomyces cerevisiae, proximity to a telomere affects both tran scription and replication of adjacent DNA. In this study, we show that telomeres also impose a position effect on mitotic recombination. The rate of recombination between directly repeated tracts of telomeric C (1-3)A/TG(1-3) DNA was reduced severely by proximity to a telomere. In contrast, recombination of two control substrates was not affected by telomere proximity. Thus, unlike position effects on transcription or replication, inhibition of recombination was sequence specific. Moreo ver, the repression of recombination was not under the same control as transcriptional repression (telomere position effect; TPE), as mutati ons in genes essential for TPE did not alleviate telomeric repression of recombination. The reduction in recombination between C(1-3)A/TG(1- 3) tracts near the telomere was caused by an absence of Rad52p-depende nt events as well as a reduction in Rad1p-dependent events. The sequen ce-specific repression of recombination near the telomere was eliminat ed in cells that overexpressed the telomere-binding protein Rap1p, a c ondition that also increased recombination between C(1-3)A/TG(1-3) tra cts at internal positions on the chromosome. We propose that the speci fic inhibition between C(1-3)A/TG(1-3) tracts near the telomere occurs through the action of a telomere-specific end-binding protein that bi nds to the single-strand TG(1-3) tail generated during the processing of recombination intermediates. The recombination inhibitor protein ma y also block recombination between endogenous telomeres.