Reactivation of avian erythrocyte nuclei in mammalian cytoplasts. A dominant role for pre-existing cytoplasmic components.

Antibodies and inhibitors have been used to study the process of nuclear reactivation following the fusion of chick erythrocytes with mouse L cell cytoplasts. Immunofluorescence results showed that a monoclonal antibody against a DNA 'tight-binding' protein from HeLa chromatin as well as an anti-Sm human serum failed to bind to the unreactivated erythrocyte nucleus, but showed strong binding after fusion. The development of antibody-binding sites was affected neither by alpha-amanitin nor by cycloheximide, indicating that some of the processes of reactivation, including specific protein uptake are independent of DNA and RNA synthesis. These results are discussed in terms of the role of the chick nucleus in directing the reactivation process.