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LOW-SALT AND HIGH-SALT RNA POLYMERASE ACTIVITY DURING PREIMPLANTATION DEVELOPMENT IN THE MOUSE

Institutes of Histology and General Embryology of the University of Rome, and of the School of Medicine of L'Aquila, Italy

(Received 29th November 1974)

In a previous paper (Siracusa, 1973) we have shown that the variations in the level of total RNA polymerase activity per embryo and per blastomere in the preimplantation mouse embryo are not correlated with patterns of RNA synthesis at corresponding stages of development. We concluded that, in the mouse embryo, in contrast with the situation found in the sea urchin embryo (Roeder & Rutter, 1970), RNA polymerase apparently does not play any direct regulatory rôle in RNA synthesis.

The possibility remained, however, that a correlation could still exist for only one of the two main forms of the enzyme. A situation of this kind has been found during the development of Rana pipiens embryos (Kohl, Norman & Brooks, 1973); Polymerase I (the nucleolar form) and Polymerase