Role of Histones in Cell Differentiation
Cell differentiation includes a variety of biological phenomena which have different characteristics and are controlled by different mechanisms. The analysis of the great number of facts and hypotheses in this field is made difficult by the different meanings given to the term cell differentiation. It has been originally proposed to describe the appearance of different specialized cells in the course of embryonic development of multicellular organisms. The reversibility and the cell-cycle independence of the functional changes suggest that such processes may be controlled by a mechanism of reversible binding of regulatory molecules to DNA similar to the phenomena of repression-derepression in prokaryotic cells. In prokaryotic cells, histones are absent but some DNA-binding proteins have been found which can induce compact structures of DNA. Histone synthesis takes place in the cytoplasm on small polyribosomes and is tightly coupled to DNA replication in all eukaryotic cells.