The structure of DNA from the rye (Secale cereale) NOR R1 locus and its behaviour in wheat backgrounds

The nucleotide sequence of a 4.5-kilobase (kb) segment of rye DNA (in the clone pScR4) containing the major spacer region of ribosomal DNA, 0.25 kb of the 5′ end of the 18S gene and approximately 1.2 kb of the 3′ end of the 26S gene is presented. The 5′ end of the 18S gene, and most of the 3′ end of the 26S gene, could be readily defined by comparisons with previously published sequences. The major spacer region was dominated by the presence of 10 repeating units, with a basic length of 134 base pairs (bp), which showed sequence variability in that deletions of sections of the sequence as well as base-pair changes were common. A portion of the sequence which was common to almost all the spacer repeats and is also found in the corresponding wheat spacer repeats (in pTa250), with only two mismatches (using a consensus sequence of the rye spacer repeats as a comparison), is GCGACATGGAAAACCGGGCAAAACCACGTAC. The occurrence of this conserved sequence between more divergent sequences in both wheat and rye sugges...