Abstract

The expression of the genes for each of the five histone proteins is tightly regulated with respect to the cell cycle, the developmental stage, and the expression of the other histone genes. In several species studied, the synthesis of all five proteins occurs exclusively in concert with the DNA synthetic phase of the cell cycle (Robbins and Borun 1967; Kedes et al. 1969; Perry and Kelley 1973); the four histones of the nucleosome core are found in equimolar amounts, whereas H1 protein is found in less than molar quantity (for review, see Kornberg 1974). Variant histone proteins associated with specific developmental stages have been observed (Cohen et al. 1975; Arceci et al. 1976; Newrock and Cohen, this volume), indicating that there must be genes for these variant proteins which are differentially expressed according to precise developmental programs. Drosophila melanogaster is an appealing organism in which to study these genes and...