The structure of the large spacer region of the rDNA in Vicia faba and Pisum sativum.

The complete nucleotide sequence of the rDNA large spacer region was determined for two related legume plants, Vicia faba and Pisum sativum. In the large spacers of both plants, there were one or several tandem arrays of repeated sequences which account well for the length heterogeneity of the rDNA repeating units. When the entire lengths of Vicia and Pisum rDNA large spacers were compared, significant sequence similarity ranging from approximately 50 to 80% was observed, thus a close phylogenetical relationship was revealed. However, organization patterns of these rDNA spacers were clearly different from each other. The Pisum rDNA large spacer contained only one type of repeated sequence of about 175 bp, whereas the Vicia contained five kinds of repeated sequence. In addition, the initiation site for transcription was tentatively determined by S1 protection experiment.