Abstract
Eukaryotic chromatin is highly dynamic and turns over rapidly even in the absence of DNA replication. Here we show that the acidic histone chaperone nucleosome assembly protein 1 (NAP-1) from yeast reversibly removes and replaces histone protein dimer H2A-H2B or histone variant dimers from assembled nucleosomes, resulting in active histone exchange. Transient removal of H2A-H2B dimers facilitates nucleosome sliding along the DNA to a thermodynamically favorable position. Histone exchange as well as nucleosome sliding is independent of ATP and relies on the presence of the C-terminal acidic domain of yeast NAP-1, even though this region is not required for histone binding and chromatin assembly. Our results suggest a novel role for NAP-1 (and perhaps other acidic histone chaperones) in mediating chromatin fluidity by incorporating histone variants and assisting nucleosome sliding. NAP-1 may function either untargeted (if acting alone) or may be targeted to specific regions within the genome through interactions with additional factors.
Highlights
The organization of DNA into chromatin has profound consequences for all processes that involve the DNA template, and the biochemical makeup of the nucleosome has important regulatory functions
We verified that yeast NAP-1 (yNAP-1) binding was not compromised by the addition of the label to H2B (Supplemental Fig. 1B) and that a yNAP-11⁄7H2A-H2B dimer complex was formed in solution (Supplemental Fig. 1C)
Upon incubation of purified nucleosome core particles (NCPs) reconstituted with fluorescently labeled H2B with increasing amounts of yNAP-1, two new bands were detected by native PAGE, and one additional band that is present in the control significantly increased in intensity
Summary
The organization of DNA into chromatin has profound consequences for all processes that involve the DNA template, and the biochemical makeup of the nucleosome has important regulatory functions. NAP-1 and other acidic histone chaperones were shown to cooperate with SWI/SNF complexes in chromatin remodeling and to facilitate transcription factor binding to nucleosomal DNA in vitro
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
