Ribosomal genes of Xenopus laevis: evidence of nucleosomes in transcriptionally active chromatin.

Most of the reiterated ribosomal genes in the somatic cells of larvae of a mutant of Xenopus laevis appear to be protected from short-term nuclease digestion by being packaged in the form of chromatin subunits or nucleosomes. Since these mutant animals probably require all of their ribosomal genes to be active in order to maintain viability, at least some of the transcriptionally active gene sequences are probably associated with chromatin subunits. Thus, association of DNA with nucleosomes may not necessarily preclude template activity, although such association is probably of a dynamic rather than a static nature.