Unusual properties of sea urchin unfertilized egg chromatin.

A typical nucleosomal pattern is not detected by electrophoretic analysis of sea urchin mature egg chromatin, following digestion with micrococcal nuclease. Moreover, at least 80% of the egg nuclear DNA is resistant to nuclease attack. These unusual features of unfertilized egg chromatin, not shared by oocytes or sperms, are discussed in view of the unique properties and fate of mature female germ cells.