Open AccessAmplified Ribosomal DNA from Xenopus laevis Has Heterogeneous Spacer Lengths
Author(s) -
Peter K. Wellauer,
Ronald H. Reeder,
Dana Carroll,
Donald D. Brown,
A H Deutch,
Toru Higashinakagawa,
Igor B. Dawid
Publication year - 1974
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.71.7.2823
Subject(s) - biology , xenopus , ribosomal dna , ribosomal rna , restriction enzyme , microbiology and biotechnology , dna , spacer dna , genetics , gene , internal transcribed spacer , restriction map , nucleic acid sequence , phylogenetics
Eco R1 restriction endonuclease makes two cuts in each repeating unit of amplified ribosomal DNA (rDNA) fromXenopus laevis . The locations of these cuts have been established by comparison of the secondary structure of single-strandedEco R1 fragments (as visualized in the electron microscope) with that ofX. laevis rRNAs and of long strands of uncut rDNA. Of the two classes of fragments generated, the smaller one contains 90% of the 28S rRNA gene, has a duplex molecular weight of 3.0 × 106 and is homogeneous in size. The larger class of molecules contains 80% of the 18S rRNA gene and all of the nontranscribed spacer. These latter fragments are heterogeneous with molecular weights ranging from 4.0 to 5.9 × 106 . The distribution of sizes within the large class of fragments varies among different preparations of rDNA, and heterogeneity is present in the DNA amplified from the rDNA of a single nucleolar organizer. The heterogeneity is located in the nontranscribed spacer region which is variable in length. This has been demonstrated by the formation of deletion loops in heteroduplexes made between larger fragments of different lengths.