Inositol phosphate kinase Vip1p interacts with histone chaperone Asf1p in Saccharomyces cerevisiae

Histone eviction and deposition are critical steps in many nuclear processes. The histone H3/H4 chaperone Asf1p is highly conserved and is involved in DNA replication, DNA repair, and transcription. To identify the factors concerned with anti-silencing function 1 (ASF1), we purified Asf1p-associated factors from the yeast Saccharomyces cerevisiae by a GST pull-down experiment, and mass spectrometry analysis was performed. Several factors are specifically associated with Asf1p, including Vip1p. VIP1 is conserved from yeast to humans and encodes inositol hexakisphoshate and inositol heptakisphosphate kinase. Vip1p interacted with Asf1p as a dimer or in a complex with another protein(s). Deletion of VIP1 did not affect the interaction between Asf1p and other Asf1p-associated factors. An in vitro GST pull-down assay indicated a direct interaction between Asf1p and Vip1p, and the interaction between the two factors in vivo was detected by an immunoprecipitation experiment. Furthermore, genetic experiments revealed that VIP1 disruption increased sensitivity to 6-azauracil (6-AU), but not to DNA-damaging reagents in wild-type and ASF1-deleted strains. It is thought that 6-AU decreases nucleotide levels and reduces transcription elongation. These observations suggest that the association of Asf1p and Vip1p may be implicated in transcription elongation.