Histones of Polytene and Nonpolytene Nuclei of Drosophila melanogaster

Polytene and nonpolytene nuclei of Drosophila melanogaster were isolated from larval salivary glands and imaginal discs, respectively. The histones of the two types of nuclei yield identical patterns on gel electrophoresis but differ considerably from those of sea urchins, birds, and mammals in the positions of F1, F2b, and possibly F3. The greatest difference is in the F1 (lysine-rich) histone, which in the case of Drosophila has a much lower electrophoretic mobility. The low mobility appears to be due to both a higher molecular weight and a lower basicity. This is the first indication of molecular weight differences between F1 histones of animals. In addition, the Drosophila F1 histone differs from mammalian F1 histones in containing a significant amount of histidine and increased amounts of serine, aspartate, valine, and isoleucine. The amino acid composition and molecular weight estimates indicate that the amount of lysine per molecule is similar to that in calf thymus F1 histone while the amounts of several other amino acids are increased. Since mammalian F1 histone is known to contain a highly basic region rich in lysine, our results suggest that the Drosophila protein may have a similar lysine-rich region, but a quite different and larger nonbasic region or regions.