Ty1 mobilizes subtelomeric Y´ elements in telomerase-negative S. cerevisiae survivors.
Patrick H. Maxwell (1), Candice Coombes (2), Alison E. Kenny (1), Joseph L. Lawler (2), Jef D. Boeke (2), M. Joan Curcio (1)
(1) Developmental Genetics, Wadsworth Center, 150 New Scotland Ave, Albany, NY, 12208, USA;
(2) Dept of Molecular Biology & Genetics, The Johns Hopkins University School of Medicine, 617 Hunterian Bldg, 725 N. Wolfe St., Baltimore, MD 21205
When telomerase is inactivated in Saccharomyces cerevisiae, telomeric DNA shortens with every cell division, and cells stop dividing after ~100 generations. Survivors that form in these senescent populations and resume growing have variably amplified arrays of a subtelomeric repeat called Y´. We marked a chromosomal Y´ element with the his3AI retrotransposition indicator gene and found that Y´HIS3 cDNA is formed and incorporated into the genome (referred to as cDNA mobility) at ~10 to 1000-fold higher frequencies in survivors compared to telomerase-positive strains. Y´ cDNA mobility is significantly reduced if assayed at 30˚C, a nonpermissive temperature for Ty1 retrotransposition, or in the absence of Tec1p, a transcription factor for Ty1. Microarray analysis revealed that Y´ RNA is preferentially associated with Ty1 virus-like particles (VLPs). Genomic copies of Y´HIS3 cDNA often have downstream oligo(A) tracts followed by downstream Ty1 sequences. Based on these findings, we suggest a model in which Ty1 cDNA intermediates are used to prime reverse transcription of polyadenylated Y´ RNA within Ty1 VLPs. We have also detected unmarked Y´-oligo(A)-Ty1 cDNA in survivors at copy numbers of ~1 x 10-2 per genome in some type I survivors. We propose that Y´-oligo(A)-Ty1 cDNA may play a role in telomere maintenance in the absence of telomerase.
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