Abstract
The yeast Y' element is a highly polymorphic repetitive sequence present in the subtelomeric regions of many yeast telomeres. The Y' element is classed as either Y'-L or Y'-S, depending on its length. It has been reported that survivors arising from telomerase-deficient yeast mutants compensate for telomere loss by the amplification of Y' elements. The total Saccharomyces cerevisiae genome DNA data base was searched for Y' elements, and 11 Y'-Ls and eight Y'-Ss were identified. As reported previously, many of the sequences were found to contain long open reading frames which potentially encode helicase. We examined the expression of the Y' elements in telomerase-deficient Deltatlc1 survivors, in which the TLC1 gene encoding the yeast telomerase template RNA had been disrupted, and found that the Y' element is highly expressed in the survivors, but not in the wild-type cells. Moreover, we demonstrated that the survivors produce a Y'-encoded protein designated as Y'-Help1 (Y'-helicase protein 1), and that this protein possesses helicase activity. Therefore, we suggest that the Y' element has a novel and potentially important role in trans, in addition to the well characterized role in cis, in telomerase-independent telomere maintenance in yeast.
Highlights
During conventional DNA synthesis, the length of the chromosomal ends or telomeres is shortened with each cell division due to the end replication problem
We systematically searched the Saccharomyces Genome Data base (SGD) for yeast YЈ-S and YЈ-L elements, and identified a total of 11 YЈ-Ls and eight YЈ-Ss in the yeast strain S288C that was used for genome sequencing
Progressive telomere shortening, senescence, and the appearance of survivors having a high degree of YЈ element amplification have been reported with est1, est2, and tlc1 mutants (15, 24, 25, this study)
Summary
During conventional DNA synthesis, the length of the chromosomal ends or telomeres is shortened with each cell division due to the end replication problem (reviewed in Ref. 1). It has been reported that survivors arising from telomerase-deficient yeast mutants compensate for telomere loss by the amplification of Y elements. These survivors still had very short stretches of terminal telomeric repeats, but, interestingly, showed high levels of amplification of the YЈ element, a repetitive sequence found in many yeast subtelomeric regions.
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