Nucleosomes Find Their Place in Life

Abstract

To carry epigenetic information, the chromatin structure must be accurately rebuilt after its deconstruction during genomic replication. Using an elegant, novel approach, Vasseur et al.[1] reveal that transcription plays a key role in sculpting the chromatin after DNA replication.

Figure 1. Chromatin maturation is driven by transcription

A. The schematic shows the movement of the replication fork on the left side of a replication bubble. The work of Vasseur et al., reveal that nucleosome positioning pattern of mature chromatin is recovered more rapidly within transcribed regions after DNA replication. This is seen in particular when the transcription template strand is on the replication template strand, rather than the newly-synthesized DNA strand, leading to differences in rates of chromatin maturation between the leading and lagging strands for many genes. ISWI and CHD1 promote nucleosome positioning, presumably by helping the histone octamers move along the DNA. HIRA enables nucleosomes to tighten their spacing, presumably via its histone removal and histone assembly activities. B. The schematic represents the same replication fork shown at the bottom of A, but with the chromatin removed, and with the leading and lagging strands indicated. The growing transcripts complementary to the transcription template strand are also shown. When the newly-synthesized DNA strand serves as the transcription template, the transcription machinery would move in the opposite direction to the replication machinery, causing a potential clash, which would be unfavorable to the cell. As a consequence, Vasseur et al., propose that transcription may be suppressed after DNA replication when the newly-synthesized DNA strands serve as transcription template strands.