THE ABILITY OF DNA AND CHROMATIN OF DEVELOPING FROG EMBRYOS TO PRIME FOR RNA POLYMERASE-DEPENDENT RNA SYNTHESIS

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Abstract
Chromatin and DNA were prepared from different stages of developing frog embryos and used as primer for RNA synthesis in a system containing RNA polymerase isolated from Micrococcus lysodeikticus. If no RNA polymerase was added, the chromatin showed relatively low priming activity which decreases from gastrula to a feeding larval stage. When RNA polymerase is added to chromatin preparations, there is an increase in priming ability during development. Chromatin preparations from later stages were found to have higher protein/DNA ratios. Dissection of embryos and isolation of chromatin from parts of embryos of a similar stage revealed differences in priming ability which did not always corrrespond to the actual amount of RNA being synthesized in vivo. Preparation of DNA from isolated nuclei of different stages revealed an increase in priming ability during the period of development studied. The protein/ DNA ratios of these preparations were essentially similar. The results of this study are discussed in relation to the concept of embryonic competence, a temporal sequence of RNA synthesis and cytodifferentiation.