Telomeres, the nucleoprotein complexes at the termini of linear chromosomes, are essential roles for end-replication, end protection, and chromatin segregation. Each process represents an obstacle for genome stability. How these problems were overcome in evolution is unknown. We have found that the highly conserved Mre11 complex is involved in telomere structure and size homeostasis. We have characterized yeast telomere chromatin structure, phenotypic heritability, and telosome segregation in both wild-type [MRE11] and a specific class of mre11 mutants. Wild-type strains confer a telomere size of 300 bp of G+T simple sequence DNA . This DNA  is embedded in a telosome: a micrococcal nuclease-resistant non-nucleosomal particle. The mre11A470Tmutation confers shorter 150 bp telomeric embedded within a telosome and is more resistant to micrococcal nuclease digestion than wild-type cells Interestingly, real-time qPCR suggests a lower or more transient binding of the mutant relative to the wild-type . Yet the introduction of wild-type Mre11 does not change the telomere size of the mutant cells and maintains the telosome structure of mutant cells. Similarly, the introduction of mre11A470T gene into a wild type genomic locus leads to a diffuse/wild-type chromatin phenotype. Our data show that telosomes predominantly restrict both MRE11  and  mre11A470T telosomes exclusively to sister chromatids, suggesting conservative segregation. To show this, we used ectopic integration to characterize cells that carry either the MRE11 or mre11A470T alleles at the genomic g%DIFDELCMD < ] %%% site, and a second opposing mre11A470T or MRE11 allele, respectively, at an ectopic site. We find that segregation of MRE11 or mre11A470T telosomes is dependent primarily on its initial genotype, but not on any subsequent genotypic change supporting the conservative segregation of a replicating chromatid
Telomeres, the nucleoprotein complexes at the termini of linear chromosomes, are essential for the processes of end replication, end-protection, and chromatin segregation. The Mre11 complex is involved in multiple cellular roles in DNA repair and structure in the regulation and function of telomere size homeostasis. In this study, we characterize yeast telomere chromatin structure, phenotypic heritability, and chromatin segregation in both wild-type [MRE11] and A470 motif alleles. MRE11 strains confer a telomere size of 300 base pairs of G+T irregular simple sequence repeats . This DNA and a portion of subtelomeric DNA is embedded in a telosome: an MNase-resistant non-nucleosomal particle. Chromatin immunoprecipitation shows a three to four-fold lower occupancy of Mre11A470T proteins than wild-type proteins in telosomes. Telosomes containing the Mre11A470T protein confer a greater resistance to MNase digestion than wild-type telosomes. The integration of a wild-type MRE11 allele into an ectopic locus in the genome of a mre11A470T mutant and the introduction of a mre11A470T %DIFDELCMD < ] %%% allele at an ectopic site in a wild-type strain lead to unexpectedly differing results. In each case, the replicated sister chromatids inherit telosomes containing only the protein encoded by the genomic mre11 locus, even in the presence of protein encoded by the opposing ectopic allele. We hypothesize that the telosome segregates by a conservative mechanism. These data support a mechanism for the linkage between sister chromatid replication and maintenance of either identical mutant or identical wild-type telosomes after replication of sister chromatids. These data suggest the presence of an active mechanism for chromatin segregation in yeast.
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roles for end-replication, end protection,
for the processes of end replication, end-protection,
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Each process represents an obstacle for genome stability. How these problems were overcome in evolution is unknown. We have found that the highly conserved
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telomere structure and
multiple cellular roles in DNA repair and structure in the regulation and function of telomere
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In this study, we characterize
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a specific class of mre11 mutants. Wild-type
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and a portion of subtelomeric DNA
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a micrococcal nuclease-resistant
an MNase-resistant
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The mre11A470Tmutation confers shorter 150 bp telomeric embedded within a telosome and is more resistant to micrococcal nuclease digestion than
Chromatin immunoprecipitation shows a three to four-fold lower occupancy of Mre11A470T proteins than
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cells Interestingly, real-time qPCR suggests a lower or more transient binding of the mutant relative to the
proteins in telosomes. Telosomes containing the Mre11A470T protein confer a greater resistance to MNase digestion than
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. Yet the introduction of
telosomes. The integration of a
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Mre11 does not change the telomere size of the mutant cells and maintains the telosome structure of mutant cells. Similarly, the introduction of mre11A470T gene into a wild type genomic locus leads to a diffuse/wild-type chromatin phenotype. Our data show that telosomes predominantly restrict both
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allele into an ectopic locus in the genome of a mre11A470T mutant
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the introduction of a
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telosomes exclusively to sister chromatids, suggesting conservative segregation. To show this, we used ectopic integration to characterize cells that carry either the MRE11 or mre11A470T alleles at the genomic
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site, and a second opposing mre11A470T or MRE11 allele, respectively, at an ectopic site. We find that segregation of MRE11 or mre11A470T telosomes is dependent primarily on its initial genotype, but not on any subsequent genotypic change supporting the conservative segregation of a replicating chromatid
allele at an ectopic site in a wild-type strain lead to unexpectedly differing results. In each case, the replicated sister chromatids inherit telosomes containing only the protein encoded by the genomic mre11 locus, even in the presence of protein encoded by the opposing ectopic allele. We hypothesize that the telosome segregates by a conservative mechanism. These data support a mechanism for the linkage between sister chromatid replication and maintenance of either identical mutant or identical wild-type telosomes after replication of sister chromatids. These data suggest the presence of an active mechanism for chromatin segregation in yeast.