We have determined the nucleotide sequence of a region of DNA derived from the end of one chromosome of the yeast, Saccharomyces cerevisiae. Inspection of the sequence reveals the presence of 12 tandem direct repeats, each 36 nucleotides long and having nearly identical sequence. Each 36 base-pair repeat can be further subdivided into three tandem sub-repeats of a similar 12 base-pair sequence. Analysis of total genomic yeast DNA from several strains by Southern hybridization suggests that the number of tandem 36 base-pair repeat units may vary from approximately 8 to 25 among different telomeric regions. Differences in the number of repeats may have arisen by unequal crossing over between them. Furthermore, the finding that the pattern of bases at multiple variable positions within the repeat unit is not random suggests that these regions may undergo gene conversion events that render them homogeneous.
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