Nucleic Acids Research

DNA from the "non-transcribed spacer" (NTS) of two wheat ribosomal RNA gene (rDNA) clones was seguenced. The regions flanking the Internal subrepeat arrays are highly conserved between the two clones; the nucleotlde sequences differ by less than one-half percent. In contrast, the consensus sequences of the subrepeats In the two arrays differ by three percent. Mutations unique to each array, yet found In more than one subrepeat of the array, are preferentially found In adjacent and alternate subrepeats. The similarity of the DNA sequences of the flanking regions Is consistent with a model of homogenlzatlon among rDNA gene units by lntergenlc conversion. We propose that a different mechanism, preferential conversion between neighboring subrepeats. Is largely responsible for the homogenlzatlon of subrepeats within an array.