Histone Chaperone Asf1 Plays an Essential Role in Maintaining Genomic Stability in Fission Yeast

Abstract

The histone H3-H4 chaperone Asf1 is involved in chromatin assembly (or disassembly), histone exchange, regulation of transcription, and chromatin silencing in several organisms. To investigate the essential functions of Asf1 in Schizosaccharomyces pombe, asf1-ts mutants were constructed by random mutagenesis using PCR. One mutant (asf1-33(ts)) was mated with mutants in 77 different kinase genes to identify synthetic lethal combinations. The asf1-33 mutant required the DNA damage checkpoint factors Chk1 and Rad3 for its survival at the restrictive temperature. Chk1, but not Cds1, was phosphorylated in the asf1-33 mutant at the restrictive temperature, indicating that the DNA damage checkpoint was activated in the asf1-33 mutant. DNA damage occured in the asf1-33 mutant, with degradation of the chromosomal DNA observed through pulse-field gel electrophoresis and the formation of Rad22 foci. Sensitivity to micrococcal nuclease in the asf1-33 mutant was increased compared to the asf1+ strain at the restrictive temperature, suggesting that asf1 mutations also caused a defect in overall chromatin structure. The Asf1-33 mutant protein was mislocalized and incapable of binding histones. Furthermore, histone H3 levels at the centromeric outer repeat region were decreased in the asf1-33 mutant and heterochromatin structure was impaired. Finally, sim3, which encodes a CenH3 histone chaperone, was identified as a strong suppressor of the asf1-33 mutant. Taken together, these results clearly indicate that Asf1 plays an essential role in maintaining genomic stability in S. pombe.

Polypeptone Induces Dramatic Cell Lysis in ura4 Deletion Mutants of Fission Yeast

“…The fission yeast, Schizosaccharomyces pombe , is a eukaryotic model organism used to study a wide range of molecular and cellular biological processes, including cell cycle regulation, signal transduction, cell polarity control, and chromatin structure [1]–[3]. S. pombe is also used to study the mechanisms responsible for controlling cell wall synthesis and cellular morphogenesis [4].…”

Structural basis for inhibition of the histone chaperone activity of SET/TAF-Iβ by cytochromec

“…Chromatin dynamics regulate transcriptional activity in response to DNA damage by promoting accessibility to DNA and serving as a docking site for repair and signaling proteins, thereby increasing repair efficiency (8,34). Recent works reveal how histone chaperones temporarily evict histones from a damaged site to facilitate access of repair factors to DNA lesions (9). However, once a DNA break is repaired, histone chaperones return histone proteins to the repaired site (35) and promote the recovery of transcriptional activity (7,13).…”

“…CPT binds covalently to Topo I and supercoiled DNA, thereby forming a ternary complex that inhibits DNA religation and generates a greater number of DSBs (37). Recently, it has been proposed that histone chaperones play a central role in chromatin disassembly connected with DNA repair and transcription recovery following DNA damage (7,9,13,35). Thus, histone chaperones such as HIRA (13), FACT (12), nucleolin (14), APLF (6) Asf1 (9), CAF-1 (10), DAXX (11), p400 (15), NAP1L1, and NAP1L4 (7) actively promote transient chromatin disorganization and histone reshaping in response to DNA damage (8).…”

“…In fact, histone chaperones have emerged as key players in the transient disorganization of chromatin required in the DNA repair process. Thus, the histone chaperones aprataxin-PNK-like factor (APLF) (6), antisilencing function 1 (Asf1) (9), chromatin assembly factor 1 (CAF-1) (10), death domain-associated protein 6 (DAXX) (11), facilitating chromatin transcription (FACT) (12), histone regulator A (HIRA) (13), nucleolin (14), p400 (15), and nucleosome assembly protein 1-like 1 (NAP1L1) and 1-like 4 (NAP1L4) (7) are recruited to damaged chromatin, thereby promoting histone dynamics in response to DNA damage. Recently, SET/TAF-1β was found to be recruited to DNA breaks to modulate the DNA damage response through the retention of certain chromatin proteins, resulting in chromatin compaction (16).…”

Sim3 shares some common roles with the histone chaperone Asf1 in fission yeast

“…We previously reported that overexpression of sim3 suppressed the temperature sensitive phenotype of the asf1–33 mutant in S. pombe [11]. In addition to the role of Sim3 as a CENP‐A Cnp1 histone chaperone that transfers CENP‐A Cnp1 protein to the center region of centromeres ( cnt , imr ), it has also been reported that Sim3 has an ability to bind histone H3 [17].…”