Structure of the two distinct types of minichromosomes that are assembled on DNA injected in Xenopus oocytes.

DNA injected into germinal vesicles of Xenopus oocytes is assembled into two distinct types of minichromosomes. One type is soluble and behaves like conventional nucleosomal chromatin. The other type is insoluble, is sensitive to DNAase I and to micrococcal nuclease, lacks a canonical nucleosome repeat, and generates a half-nucleosome size limit digest with micrococcal nuclease. We suggest that these peculiar minichromosomes may be the ones that display the unconstrained, "dynamic" DNA supercoils in the living oocyte.