Nucleosomes and nonribosomal RNA transcription in early mouse embryo. An electron microscopic study.

Zygotes from hyperovulated albino-mice isolated during the first several cleavages were spread according to the method of Miller and Bakken [28] in the presence and in the absence of Joy or in the presence of Sarcosyl. Our results show that: 1. already before the first division of the mouse zygote all chromatin is organized in nucleosomes, 2. nonribosomal RNA transcription starts during the first divisions, 3. chromatin fibers associated with nonribosomal RNA transcription have a nucleosomal structure and 4. the use of detergent Joy may destroy the nucleosomes of some chromatin fibers.