Chromosome healing through terminal deletions generated by de novo telomere additions in Saccharomyces cerevisiae

Abstract

Broken chromosomes healed by de novo addition of a telomere are a major class of genome rearrangements seen in Saccharomyces cerevisiae and similar to rearrangements seen in human tumors. We have analyzed the sequences of 534 independent de novo telomere additions within a 12-kb region of chromosome V. The distribution of events mirrored that of four-base sequences consisting of the GG, GT, and TG dinucleotides, suggesting that de novo telomere additions occur at short regions of homology to the telomerase guide RNA. These chromosomal sequences restrict potential registrations of the added telomere sequence. The first 11 nucleotides of the addition sequences fell into common families that included 91% of the breakpoints. The observed registrations suggest that the 3 end of the TLC1 guide RNA is involved in annealing but not as a template for synthesis. Some families of added sequences can be accounted for by one cycle of annealing and extension, whereas others require a minimum of two. The same pattern emerges for sequences added onto the most common addition sequence, indicating that de novo telomeres are added and extended by the same process. Together, these data indicate that annealing is central to telomerase registration, which limits telomere heterogeneity and resolves the problem of synthesizing Rap1 binding sites by a nonprocessive telomerase with a lowcomplexity guide RNA sequence.

Saccharomyces cerevisiae as a Model System To Define the Chromosomal Instability Phenotype

“…A similar distribution is observed for de novo telomere additions (see Fig. S1 in the supplemental material) that target short TG-rich regions during the healing of broken chromosomes (83).…”

Smc5–Smc6 complex suppresses gross chromosomal rearrangements mediated by break-induced replications

“…The suppression mechanisms include cell cycle checkpoints [7][8][9][10][11][12], post-replication [13,14] and mismatch repair [15,16], recombination pathways, an anti-de novo telomere addition mechanism [17,18], chromatin assembly factors [11,19], mechanisms that prevent end-to-end chromosome fusions [17,18,20] and a pathway detoxifying reactive oxygen species [14,21,22]. In contrast, the promoters of GCRs include telomerase-related factors [17,23], a mitotic checkpoint network [24], the Rad1-Rad10 endonuclease [25], non-homologous end-joining proteins including Lig4 and Nej1 [17], a pathway generating inappropriate recombination via sumoylation and the Srs2 helicase [13] and the Bre1 ubiquitin ligase [13].…”

Cellular and molecular effects of nonreciprocal chromosome translocations in Saccharomyces cerevisiae

“…Translocations and other gross chromosomal rearrangements (GCRs), i.e., deletions and inversions, are often observed in cancer cells (6). Recently, seven pathways that suppress (7)(8)(9) and four pathways that are required for the formation of GCRs (10)(11)(12) have been identified in yeast. From the great number and redundancy of factors involved in GCR suppression, it can be concluded that any genomic rearrangement is highly deleterious to cells, and, once escaped from control, it can have a massive impact on cellular morphology and physiology.…”