Replication-independent histone deposition by the HIR complex and Asf1.

The orderly deposition of histones onto DNA is mediated by conserved assembly complexes, including chromatin assembly factor-1 (CAF-1) and the Hir proteins . CAF-1 and the Hir proteins operate in distinct but functionally overlapping histone deposition pathways in vivo . The Hir proteins and CAF-1 share a common partner, the highly conserved histone H3/H4 binding protein Asf1, which binds the middle subunit of CAF-1 as well as to Hir proteins .

Histone deposition protein Asf1 maintains DNA replisome integrity and interacts with replication factor C.

Chromatin assembly and DNA replication are temporally coupled, and DNA replication in the absence of histone synthesis causes inviability. Here we demonstrate that chromatin assembly factor Asf1 also affects DNA replication. In budding yeast cells lacking Asf1, the amounts of several DNA replication proteins, including replication factor C (RFC), proliferating cell nuclear antigen (PCNA), and DNA polymerase epsilon (Pol epsilon), are reduced at stalled replication forks.

Structure and function of the conserved core of histone deposition protein Asf1.

Background: Asf1 is a ubiquitous eukaryotic histone binding and deposition protein that mediates nucleosome formation in vitro and is required for genome stability in vivo. Studies in a variety of organisms have defined Asf1's role as a histone chaperone during DNA replication through specific interactions with histones H3/H4 and the histone deposition factor CAF-I. In addition to its role in replication, conserved interactions with proteins involved in chromatin silencing, transcription, chromatin remodeling, and DNA repair have also established Asf1 as an important component of a number of chromatin assembly and modulation complexes.

Defective S phase chromatin assembly causes DNA damage, activation of the S phase checkpoint, and S phase arrest.

The S phase checkpoint protects the genome from spontaneous damage during DNA replication, although the cause of damage has been unknown. We used a dominant-negative mutant of a subunit of CAF-I, a complex that assembles newly synthesized DNA into nucleosomes, to inhibit S phase chromatin assembly and found that this induced S phase arrest. Arrest was accompanied by DNA damage and S phase checkpoint activation and required ATR or ATM kinase activity.

Chromatin assembly factor I and Hir proteins contribute to building functional kinetochores in S. cerevisiae.

Budding yeast centromeres are comprised of approximately 125-bp DNA sequences that direct formation of the kinetochore, a specialized chromatin structure that mediates spindle attachment to chromosomes. We report here a novel role for the histone deposition complex chromatin assembly factor I (CAF-I) in building centromeric chromatin. The contribution of CAF-I to kinetochore function overlaps that of the Hir proteins, which have also been implicated in nucleosome formation and heterochromatic gene silencing.