Heterochromatin is typically highly condensed, gene-poor,
and transcriptionally silent, whereas euchromatin is less
condensed, gene-rich, andmore accessible to transcription.
Besides acting as a graveyard for selfish mobile DNA repeats,
heterochromatin contributes to important biological
functions, such as chromosome segregation during cell
division. Multiple features of heterochromatin—including
the presence or absence of specific histone modifications,
DNAmethylation, andsmallRNAs—have beenimplicated
in distinguishing heterochromatin from euchromatin in
various organisms. Cells malfunction if the genome fails
to restrict repressive chromatin marks within heterochromatin
domains. How euchromatin and heterochromatin
territories are confined remains poorly understood. Recent
studies from the fission yeast Schizosaccharomyces
pombe, the flowering plant Arabidopsis thaliana, and the
filamentous fungusNeurospora crassa have revealed a new
role for Jumonji C (JmjC) domain-containing proteins in
protecting euchromatin from heterochromatin marks.
Heterochromatin is typically highly condensed, gene-poor,
and transcriptionally silent, whereas euchromatin is less
condensed, gene-rich, andmore accessible to transcription.
Besides acting as a graveyard for selfish mobile DNA repeats,
heterochromatin contributes to important biological
functions, such as chromosome segregation during cell
division. Multiple features of heterochromatin—including
the presence or absence of specific histone modifications,
DNAmethylation, andsmallRNAs—have beenimplicated
in distinguishing heterochromatin from euchromatin in
various organisms. Cells malfunction if the genome fails
to restrict repressive chromatin marks within heterochromatin
domains. How euchromatin and heterochromatin
territories are confined remains poorly understood. Recent
studies from the fission yeast Schizosaccharomyces
pombe, the flowering plant Arabidopsis thaliana, and the
filamentous fungusNeurospora crassa have revealed a new
role for Jumonji C (JmjC) domain-containing proteins in
protecting euchromatin from heterochromatin marks.
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