- Günther Bretzel: Institut für Molekularbiologie und Biochemie, Freie Universiät Berlin, Arnimallee 22, D-1000, Berlin 33.
- Hildegard Tiedemann: Institut für Molekularbiologie und Biochemie, Freie Universiät Berlin, Arnimallee 22, D-1000, Berlin 33.
From embryos (Xenopus laevis) of different developmental stages nuclei were isolated which exert neural inducing activity in the biological test. The active material could partly be extracted from the nuclei. Experiments for the isolation of nuclear ribonucleoprotein (RNP) particles have shown that the activity is localized at least in part in these particles. On the other hand, some neural inducer is not detached from chromatin and the nuclear matrix even with ionic detergents. Inducing activity was found in germinal vesicles and to a higher degree in the cytoplasm of oocytes, but in a masked, biologically inactive state.