THE RELATIONSHIP BETWEEN RNA SYNTHESIS AND LOOP STRUCTURE IN LAMPBRUSH CHROMOSOMES

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Abstract
Ribonucleic acid synthesis in lampbrush chromosomes occurs on loops which project from the main axis of the chromosome. These loops contain DNA in addition to RNA. The synthesis of RNA in the chromosome is a DNA-dependent process, as judged by its sensitivity to inhibition by Actino-mycin D. Nucleolar RNA synthesis is also blocked by this antibiotic. The addition of Actinomycin D to isolated chromosomes, or to intact oocytes, not only inhibits RNA synthesis, but also leads to a disappearance of the chromosomal loops. A modified Actinomycin C3 (which does not block RNA synthesis) does not cause loop retraction. Other agents which inhibit nuclear RNA synthesis, such as the arginine-rich histones, also cause the loops to disappear. Inhibitors of protein synthesis, such as puromycin, do not have this effect. The results suggest that the morphology of an active chromosomal site is not only closely related to its capacity to synthesize RNA, but is dependent upon it.