Chromatin alteration, transcription and replication: What's the opening line to the story?

Polymerase accessibility to chromatin is a limiting step in both RNA and DNA synthesis. Unwinding DNA and nucleosomes during polymerase complex binding and processing likely requires priming by chromatin restructuring. The initiating step in these processes remains an area of speculation. This review focuses on the physical handling of chromatin during transcription and replication, the fate of nucleosomes assembled on DNA during unwinding and processing the chromatin substrate, and how these alterations in chromatin structure may affect gene expression. Transcription or replication may alter chromatin structure during synthesis, enabling regulatory factor binding and, potentially, future rounds of transcription. As chromatin remodeling and transcription factor binding augment transcription and replication, and are themselves increased by these processes, a temporal model of structural alterations and gene activation is built that may be more circular than linear.