Time course of polynucleosome relaxation and ADP‐ribosylation

Abstract

Isolated rat pancreatic polynucleosomes were poly(ADP-ribosylated) with purified calf thymus poly(ADP-ribose) polymerase. A time course study was performed using an NAD concentration of 200 .mu.M and changes in nucleosomal structure were investigated by means of EM visualization and sedimentation velocity determinations. In parallel, analyses of histone H1 poly(ADP-ribosylation) and determinations of DNA polymerase .alpha. activity on ADP-ribosylated polynucleosomes were done at different time intervals. A direct kinetic correlation between ADP-ribose incorporation, polynucleosome relaxation and histone H1 hyper-ADP-ribosylation was established. In addition, DNA polymerase .alpha. activity was highly stimulated on ADP-ribosylated polynucleosomes as compared to control ones, suggesting increased accessibility of DNA to enzymatic action. Because of the strong evidence implicating histone H1 in the maintenance of higher-ordered chromatin structures, this study may provide a basis for the interpretation of the involvement of the histone H1 ADP-ribosylation reaction in DNA rearrangements during DNA repair, replication or gene expression.