THE MOLECULAR DIVERSITY OF THE 5S RIBOSOMAL-RNA GENE IN BARLEY (HORDEUM-VULGARE)

The 5S rDNA genes from several accessions of cultivated barley, Hordeum vulgare L., were amplified by the polymerase chain reaction, cloned, and sequenced. Analysis of the aligned sequences, followed by principal coordinate analysis, support the recognition of at least two distinct classes of 5S rDNA genes. The short repeat class corresponds to the 300-bp tandem repeat defined by E.V. Ananiev as containing several TAG repeating units. The long repeat class contains long tandem repeats and lacks the TAG repeating unit. Sequences in each class can be further subdivided, with the long repeat class containing two groups and the short repeat class containing two and possibly three groups. These results suggest that in cultivated barley the sequence diversity found within the 5S rDNA nontranscribed spacer region may be encoded by three or more loci and may be useful for phylogenetic analyses provided that orthology can be established.