An acidic protein which assembles nucleosomes in vitro is the most abundant protein in Xenopus oocyte nuclei

Eggs and oocytes of the frog Xenopus laevis contain an acidic thermostable protein which promotes assembly of nucleosomes from histones and DNA in vitro (Laskey et al., 1978). Analysis of the abundance and intracellular distribution of this protein reveal that it is exclusively localized within the oocyte nucleus where it is the most abundant protein. Its intranuclear concentration is 5 to 7 mg/ml representing 7 to 10% of the total nuclear protein. Micro-injection into oocyte cytoplasm demonstrates that the property of intranuclear migration resides in the mature protein. The injected protein migrates into the nucleus efficiently and becomes distributed throughout the nucleoplasm but it does not associate preferentially with structures containing DNA.