DNA-protein cross-linking in nuclei of immature and mature chicken erythrocytes

DNA-protein cross-linkages were formed in isolated nuclei from immature and mature chicken erythrocytes by reaction with cis-diammine dichloroplatinum . On the basis of electrophoretic behaviour, the most abundant proteins inv olved in the cross-linking appeared to be present also in preparations of n uclear matrix. The maturation of the erythrocyte, which is accompanied by t ranscriptional inactivation, leads to a decrease in the amount of DNA-inter acting proteins, to a loss of proteins capable of a specific recognition of DNA sequences and, unexpectedly, to the appearence of some new DNA-protein interactions. At least three cross-linked proteins were found predominantl y or exclusively in nuclei of immature cells, and three others in those of mature ones. The three DNA-bound proteins, typical of mature erythrocytes, were not found among the components of a high-salt preparation of nuclear m atrix. The results obtained suggest that, in addition to the well-known histone H5 and MENT protein, these newly identified DNA-bound proteins contribute to the formation of the condensed, inactive chromatin characteristic of mature erythrocyte.