The percentage of the incorporation of tritiated leucine into nuclear proteins has been investigated at various stages of sea urchin development. The results indicate a non-coincidence in the requirement for histones and nonhistone proteins. The results are consistent with the hypothesis of a modulation of gene activity based on histone/non-histone interaction influencing the nature and the strength of the ionic histone to DNA binding. In addition, evidence is offered that newly synthesized messenger RNA's are richer in nuclear protein messengers than the maternal ones.