Diffusible and bound actin nuclei of Xenopus laevis oocytes

Several criteria have been used to identify actin in hand-isolated nuclei of Xenopus laevis oocytes; these include co-migration with actin on SDS-polyacrylamide gels, immunological cross-reactivity with antiserum against actin, binding to DNAase I and peptide mapping on SDS gels. The use of hand-isolated nuclei precludes the possibility of contamination from cytoplasmic actin or the leakage of significant amounts of actin from nuclei during isolation. Actin constitutes roughly 6% of the total nuclear protein. Approximately 75% of the actin is diffusible under the conditions of nuclear isolation used. About 25%, however, is stably associated with an insoluble nuclear gel, in which chromosomes, nucleoli and other nuclear granules are embedded. Actin is the single most promient component of the nuclear gel, comprising roughly 16% of the total protein of the complex. The possible significance of diffusible and bound actin in these nuclei is discussed.