Specific Conformations and Interactions in Chicken Erythrocyte Histone F2C

Abstract

THE close association of histones with DNA in the eukaryote chromosome has implicated them in two possible functions; first, a structural role in maintaining and controlling the conformations of the chromosome through the cell cycle, and second, involvement in genetic control mechanisms¹. The relatively small number of histones and the rigid conservation of sequence found for histone F2A1 (see ref. 2) and suspected for other histones argue more for a structural role and involvement in the gross repression of inactive genes than for a role in the precise control of active genes. The sequence studies of histones^2–6 have delineated well defined regions of the chain, rich either in basic and helix-destabilizing residues or rich in apolar, acidic and aromatic residues. Physical studies^7–11 have demonstrated that the later regions are the sites of secondary structure and histone-histone interaction, while the former are the sites of DNA interaction. Thus, although particular regions of the histone chains have been correlated with quite different functions, there has been no evidence so far to show that the relatively non-basic segments fold up so specifically as in globular proteins. If, however, histones are involved in controlling the conformation of chromosomes, then specific and reversible interactions are to be expected. The very lysine-rich histones are distinguished from other histones in that microheterogeneity has been found for F1 (refs. 12–14), while F2C is polymorphic¹⁵, and it has been suggested that they have a function additional to structural. Histone F2C is unique to nucleated erythrocytes¹⁶, largely replacing F1 therein and could be involved in the total repression of erythrocyte genes.