Organisation of genes for ribosomal RNA in Physarum polycephalum

Physarum polycephalum nucleolar satellite DNA has been analysed by restriction enzyme digests and hybridisation to ribosomal RNA. The nucleolar DNA is isolated as molecules of molecular weight 39 X 10(6). The positions of sites of endo R-EcoRI and endo R-HindIII digestion have been determined accurately in the whole molecule. The endo R-EcoRI sites and one endo R-HindIII site are within the26-S rRNA complementary sequence and the other endo R-HindIII site is within the 19-S rRNA complementary sequence. The sites are arranged symmetrically about the centre of the molecule as if it were a palindrome.