Topographical analysis of yeast ribosomal DNA by cleavage with restriction endonucleases. II. The physical map of EcoRI fragments.

Yeast ribosomal DNA (rDNA) was digested with the restriction endonuclease EcoRI. Eight distinct fragments were obtained with a molecular weight of 4.35 (1), 1.75 (2), 1.45 (3), 1.07 (4), 0.42 (5), 0.37 (6), 0.26 (7) and 0.22 x 10(6) (8) daltons, respectively. Except for fragment 1 with a molecular weight of 4.35 x 10(6) daltons, all fragments are derived from the multiple ribosomal transcription units. The 'spacer' sequences, on the other hand, gave rise to digestion products which are very heterogeneous in size. By analysis of the partial digestion products which are very heterogeneous in size. By analysis of the partial digestion products, together with the data obtained by digestion with a combination of two restriction enzymes (EcoRI and Hind II or Hind III) and redigestion of the Hind II-and Hind III-fragments with EcoRI, the physical map of the EcoRI cleavage sites in the ribosomal transcription unit could be established.