Signal transduction pathways converge upon sequence-specific DNA binding factors to reprogram gene expression. Transcription factors, in turn, team up with chromatin modifying activities. However, chromatin is not simply an endpoint for signaling pathways. Histone modifications relay signals to other proteins to trigger more immediate responses than can be achieved through altered gene transcription, which might be especially important to time-urgent processes such as the execution of cell-cycle check points, chromosome segregation, or exit from mitosis. In addition, histone-modifying enzymes often have multiple nonhistone substrates, and coordination of activity toward different targets might direct signals both to and from chromatin.
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