The fate of heterologous DNA microinjected into eggs of amphibians during their development. II. Investigations by centrifugal chromatography on DEAE-cellulose paper pulp, ultracentrifugation in CsCl gradient and DNA-DNA hybridization in agar gel

The fate of heterologous DNA microinjected into eggs of amphibians has been studied using the following methods: 1. 1. Fractionation on columns of centrifuged DEAE-cellulose paper pulp. 2. 2. Ultracentrifugation in CsCl gradient. 3. 3. Hybridization in agar gel. It has been found that highly polymerized ²H-labelled DNA from Escherichia coli injected into eggs of Pleurodeles at the stage of 2 or 4 blastomeres seemed to resist depolymerization and to preserve to an extent of about 90 % its primary and secondary structure during cleavage, which leads to the stage of blastula (i.e., when the injection of DNA did not provoke the complete inhibition of the embryo development). When injected at the blastula stage (into the blastocoel cavity) a part of ³H-labelled DNA still seemed to retain its primary and secondary structure three days after the injection. The more highly polymerized the DNA at the beginning, the more likely it was that it would be undegraded after this time. In the case of injections at the blastula stage the amount of heterologous, non-depolymerized DNA remaining in the embryo was higher when determined by ultracentrifugation than by the hybridization method. The total radioactivity injected into the eggs falls gradually during their development.