Alternative titles; symbols
HGNC Approved Gene Symbol: CHAF1A
Cytogenetic location: 19p13.3 Genomic coordinates (GRCh38): 19:4,402,640-4,450,830 (from NCBI)
Chromatin assembly factor I (CAF1) is a nuclear complex consisting of p50, p60 (CHAF1B; 601245), and p150 (CHAF1A) subunits that assembles histone octamers onto replicating DNA in vitro (Kaufman et al., 1995).
Kaufman et al. (1995) obtained a cDNA for the p150 CAF1 subunit by using a combination of antibody screening of an expression library and partial protein sequencing. The predicted 938-amino acid protein appears to be highly charged and has an isoelectric point of 5.5. It has a PEST (proline-glutamic acid-serine-threonine) box near the N terminus that is associated with proteins of short half-lives.
Kaufman et al. (1995) found that the p150 and p60 CAF1 subunits interacted with each other in nucleosome assembly, and deletion of the p60-binding domain (amino acids 642 to 677) from p150 abolished chromatin assembly. They also showed that p150 and p60 formed complexes with newly synthesized histone H3 (see 601058) and acetylated histone H4 (see 602822), which may form an intermediate prior to assembly on replicating DNA.
Murzina et al. (1999) demonstrated that CHAF1A binds to mouse heterochromatin-binding protein-1 (Hp1; see 604478) via an N-terminal domain. Mutations in CHAF1A prevented association with Hp1 in heterochromatin in cells that were not in S phase and the formation of CHAF1-Hp1 complexes in nascent chromatin during DNA replication in vitro. These data suggested that CHAF1A has a heterochromatin-specific function distinct from its nucleosome assembly function during S phase. Just before mitosis, CHAF1A and some HP1 progressively dissociate from heterochromatin concomitant with histone H3 phosphorylation. The HP1 proteins reassociate with chromatin at the end of mitosis, as histone H3 is dephosphorylated.
Using small interfering RNA, Hoek and Stillman (2003) found that knockdown of CAF1 p150 in human cell lines resulted in cells that accumulated in early and mid S phase and replicated DNA slowly. The checkpoint kinase CHK1 (CHEK1; 603078), but not CHK2 (CHEK2; 604373), was phosphorylated in response to CAF1 depletion, consistent with a DNA replication defect. CAF1-depleted cell extracts completely lacked DNA replication-coupled chromatin assembly activity. Hoek and Stillman (2003) concluded that, in contrast to yeast, human CAF1 is necessary for coupling chromatin assembly with DNA replication.
To elucidate regulatory pathways that safeguard the somatic state, Cheloufi et al. (2015), performed 2 comprehensive RNA interference (RNAi) screens targeting chromatin factors during transcription factor-mediated reprogramming of mouse fibroblasts to induced pluripotent stem cells (iPS cells). Subunits of the CAF1 complex, including Chaf1a and Chaf1b, emerged as the most prominent hits from both screens, followed by modulators of lysine sumoylation and heterochromatin maintenance. Optimal modulation of both CAF1 and transcription factor levels increased reprogramming efficiency by several orders of magnitude and facilitated iPS cell formation in as little as 4 days. Mechanistically, CAF1 suppression led to a more accessible chromatin structure at enhancer elements early during reprogramming. These changes were accompanied by a decrease in somatic heterochromatin domains, increased binding of Sox2 (184429) to pluripotency-specific targets, and activation of associated genes. Notably, suppression of CAF1 also enhanced the direct conversion of B cells into macrophages and fibroblasts into neurons. The findings of Cheloufi et al. (2015) revealed the histone chaperone CAF1 to be a novel regulator of somatic cell identity during transcription factor-induced cell fate transitions and provided a potential strategy to modulate cellular plasticity in a regenerative setting.
Cheloufi, S., Elling, U., Hopfgartner, B., Jung, Y. L., Murn, J., Ninova, M., Hubmann, M., Badeaux, A. I., Ang, C. E., Tenen, D., Wesche, D. J., Abazova, N., and 24 others. The histone chaperone CAF-1 safeguards somatic cell identity. Nature 528: 218-224, 2015. [PubMed: 26659182] [Full Text: https://doi.org/10.1038/nature15749]
Hoek, M., Stillman, B. Chromatin assembly factor 1 is essential and couples chromatin assembly to DNA replication in vivo. Proc. Nat. Acad. Sci. 100: 12138-12188, 2003.
Kaufman, P. D., Kobayashi, R., Kessler, N., Stillman, B. The p150 and p60 subunits of chromatin assembly factor I: a molecular link between newly synthesized histones and DNA replication. Cell 81: 1105-1114, 1995. [PubMed: 7600578] [Full Text: https://doi.org/10.1016/s0092-8674(05)80015-7]
Murzina, N., Verreault, A., Laue, E., Stillman, B. Heterochromatin dynamics in mouse cells: interaction between chromatin assembly factor 1 and HP1 proteins. Molec. Cell 4: 529-540, 1999. [PubMed: 10549285] [Full Text: https://doi.org/10.1016/s1097-2765(00)80204-x]