Effect of poly(ADP-ribosyl)ation and Mg2+ ions on chromatin structure revealed by scanning force microscopy.
Poly(ADP-ribosyl)ation of nuclear proteins is responsible for major changes in the high-order chromatin structure. The effects of this post-translation modification on nuclear architecture were examined at different Mg2+ concentrations using scanning force microscopy. A quantitative analysis of the internucleosomal distance, the width, and the volume of chromatin fibers imaged in tapping mode reveals that poly(ADP-ribosyl)ation induces a complete relaxation and decondensation of the chromatin structure. Our data, on the center-to-center distance between adjacent nucleosomes and on the fiber width, indicate that the poly(ADP-ribosyl)ated fibers remain significantly decondensed even in the presence of Mg2+. Our results also show that the Mg2+ assumes an important role in the folding of chromatin structure, but Mg2+ is not able to restore the native feature of chromatin, when the fibers are depleted of H1/H5 histones. The combined effect of post-translation modification and cation ions on the chromatin structure shows that poly(ADP-ribosyl)ation could promote accessibility to DNA even in those nuclear processes that require Mg2+.
d'Erme
M
M
Department of Biochemical Sciences, University of La Sapienza, P.le A. Moro 5, I-00185 Roma, Italy. maria.derme@uniroma1.it
Yang
G
G
Sheagly
E
E
Palitti
F
F
Bustamante
C
C
D002843:Chromatin / Q000648:ultrastructure*; D006657:Histones / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D008968:Molecular Conformation; D009707:Nucleosomes / Q000648:ultrastructure; D011064:Poly Adenosine Diphosphate Ribose / Q000378:metabolism*; D011499:Protein Processing, Post-Translational
D002843:Chromatin; D006657:Histones; D009707:Nucleosomes; D011064:Poly Adenosine Diphosphate Ribose; D008274:Magnesium