Unusual DNA sequences associated with the ends of yeast chromosomes

The genome of the yeast Saccharomyces cerevisiae, like those of other eukaryotes, contains multiple sequences that hybridize with a poly(GT) probe. We have shown previously that some of the sequences that hybridize with the poly(GT) probe are located near the tips of the yeast chromosomes. We report here that many of the remaining poly(GT)-hybridizing sequences are associated with a family of putative replication origins localized near the chromosome ends. These sequences have the general form poly(C1-3A), similar to sequences reported to occur at the tips of chromosomes in the accompanying paper. In addition to poly(C1-3A) tracts, yeast cells contain tracts of alternating C and A bases, similar to those seen in mammalian genomes. These results are used as the basis for a new model of telomere replication.