A histone-binding protein, nucleoplasmin, stimulates transcription factor binding to nucleosomes and factor-induced nucleosome disassembly.

The binding of a GAL4-AH, USF or Sp1 to nucleosome cores was stimulated by the presence of the histone-binding protein, nucleoplasmin. Stimulation of factor binding by nucleoplasmin was specific for nucleosome reconstituted DNA and was not mimicked by non-specific histone sinks (i.e. polyglutamate or RNA). Upon GAL4-AH binding, nucleoplasmin specifically removed histones H2A and H2B from the nucleosome which enhanced the subsequent loss of the H3/H4 tetramers onto competing DNA. Thus, nucleoplasmin participated in the complete conversion of nucleosome cores to transcription factor-DNA complexes. These data indicate that proteins which bind histones can increase transcription factor binding to nucleosomal DNA and that transcription factor binding can initiate nucleosome disassembly. Similar activities of histone-binding proteins may participate in the displacement of nucleosomes at enhancers and promoters in vivo.