High impact information on ASF1

• Using purified, recombinant proteins, we demonstrate that RFC directly binds Asf1 and can recruit Asf1 to DNA molecules in vitro [1].
• Here we demonstrate that chromatin assembly factor Asf1 also affects DNA replication [1].
• The deletions of CAC1 (cac1Delta), ASF1 (asf1Delta), and SAS2 (sas2Delta) had similar effects on gene silencing and were partially overlapping [2].
• In this study, the MYST family acetyltransferase Sas2 was found to interact with Cac1, the largest subunit of Saccharomyces cerevisiae chromatin assembly factor-I (CAF-I), and with the nucleosome assembly factor Asf1 [2].
• The silencing complex SAS-I links histone acetylation to the assembly of repressed chromatin by CAF-I and Asf1 in Saccharomyces cerevisiae [2].

Biological context of ASF1

• Thus, ASF1-dependent chromatin assembly may mediate the role of the SAS complex in silencing [3].
• Yeast ASF1 protein is required for cell cycle regulation of histone gene transcription [4].
• These phenotypes suggested a role for ASF1 in DNA repair and chromosome maintenance [5].
• The ASF1 protein was evolutionarily conserved, MCB motifs, sequences commonly present upstream of genes transcribed specifically in S phase, were found in front of both genes, and, indeed, both genes were transcribed specifically in the S phase of the cell cycle [5].
• Two new yeast genes, ASF1 (Anti-Silencing Function) and ASF2, as well as a C-terminal fragment of SIR3, were identified as genes that derepressed the silent mating type loci when overexpressed [5].

Associations of ASF1 with chemical compounds

• The asf1 mutant was sensitive to methyl methane sulfonate, slightly UV-sensitive and somewhat deficient in minichromosome maintenance [5].
• By contrast, deletion of ASF1 has no effect on the S-phase specific peak of H4 lysine 12 acetylation; another modification carried by newly synthesized histones prior to chromatin assembly [6].

Physical interactions of ASF1

• Also, Asf1p bound to the Hir1p and Hir2p proteins in vitro and in cell extracts [7].
• These data suggest that the HAT activity and ASF1-dependent localization of the SAS complex are required for SIR1-dependent HMLalpha silencing [8].
• Chromatin assembly factor I mutants defective for PCNA binding require Asf1/Hir proteins for silencing [9].
• Histone deposition protein Asf1 maintains DNA replisome integrity and interacts with replication factor C [1].

Regulatory relationships of ASF1

• In vivo, Asf1p and Hir proteins physically interact and together promote heterochromatic gene silencing in a manner requiring PCNA [7].
• This Asf1p/H3/H4 complex generated micrococcal nuclease--resistant DNA in the absence of DNA replication and stimulated nucleosome assembly activity by recombinant yeast CAF-I during DNA synthesis [7].
• These substitution mutations spared the basal interaction with Asf1 and the DNA damage-induced interactions with Rad9 [10].
• Epistasis analysis indicates that the histone H3 and HAT1 mutants may influence DNA double-strand break repair through Asf1p-dependent chromatin assembly [11].
• Here we report that overproduction of the chromatin assembly factor Asf1 can suppress the Ts phenotype of mrc1rad53 double mutants and the HU sensitivity of rad53 mutants [12].

Other interactions of ASF1

• In contrast to the effects of disrupting ASF1 and CHD1, deletion of SNF2 is associated with increased resistance of chromatin to digestion by micrococcal nuclease [13].
• In vivo, the HIR1 and ASF1 genes contributed to silencing the heterochromatic HML locus via the same genetic pathway [7].
• ASF2 overexpression caused a greater derepression than did ASF1 [5].
• Furthermore, increased expression of genes encoding Asf1p, Hir1p, and Hir2p suppressed the apc5(CA) Ts- defect in a CAF-I-dependent manner [14].
• Conversely, other pol30 alleles prevented Asf1/Hir proteins from contributing to silencing [7].

References