Chromatin fibers organization within the nucleus

In order to evaluate at the ultrastructural level the three dimensional arr angement of the dispersed chromatin during the intephase, the immunogold de tection of Bromodeoxyuridine (BrdU), of the DNA polymerase alpha and of the proliferating cell nuclear antigen (PCNA) was performed on human HL60 leuk emia cells and nuclear matrices extracted from the same cellular model. The Field Emission In lens Scanning Electron Microscopy analysis of the ultrat hin cryosectioned cells revealed the presence of a chromatin three dimensio nal network where the different constituents appeared repetitively assemble d. Also the nuclear matrix showed a repetitive structure, on which the depr ivation of the DNA corresponded to the selective loss of particular class s ized fibers. The single or multiple combined immunolocalization of differen t structures involved in the DNA replication,where BrdU, DNA polymerase alp ha and PCNA represent, respectively, the substratum, the polymerizing enzym e and a regulator of the reaction, allowed the understanding of its recipro cal spatial relationship on the dispersed interphasic chromatin and the rol e of the nuclear matrix in the replicative process.