The structure of the rDNA intergenic spacer of Avena sativa L.: a comparative study

The sequence of the 18S–25S ribosomal RNA gene intergenic spacer (IGS) of Avena sativa was determined. DNA was cloned after polymerase chain reaction amplification of the IGS. The spacer of 3980 bp is composed of non-repeated sequences and five tandem arrays of repeated sequences, named A to E. Homology between oats IGS and other grass species was found. Tandem arrays D and E seem to be originated by duplication from single-copy sequences in related species. A transcription initiation site and putative sites of termination, processing and methylation were detected by computer-aided search. These sites resemble motifs conserved in the IGS of plant species.