DNA repair factor APLF acts as a H2A-H2B histone chaperone through binding its DNA interaction surface

Abstract

Genome replication∗transcription and repair require the assembly/disassembly of the nucleosome Histone chaperones are regulators of this process by preventing formation of non-nucleosomal histone-DNA complexes Aprataxin and polynucleotide kinase like factor (APLF) is a non-homologous endjoining (NHEJ) DNA repair factor that possesses histone chaperone activity in its acidic domain (APLFAD) Here∗we studied the molecular basis of this activity using biochemical and structural methods We find that APLFAD is intrinsically disordered and binds histone complexes (H3-H4)2 and H2A-H2B specifically and with high affinity APLFAD prevents unspecific complex formation between H2A-H2B and DNA in a chaperone assayvestablishing for the first time its specific histone chaperone function for H2AH2B On the basis of a series of nuclear magnetic resonance studies∗supported by mutational analysis∗we show that the APLFAD histone binding domain uses two aromatic side chains to anchor to the 1-2 patches on both H2A and H2B∗thereby covering most of their DNA-interaction surface An additional binding site on both APLFAD and H2A-H2B may be involved in the handoff between APLF and DNA or other chaperones Together∗our data support the view that APLF provides not only a scaffold but also generic histone chaperone activity for the NHEJ-complex.