Length heterogeneity of the large spacer of Vicia faba rDNA is due to the differing number of a 325 bp repetitive sequence elements

Summary The DNA fragments including the whole large spacer region of Vicia faba rDNA were cloned in plasmid pBR325. Sixteen clones were classed into five groups which differed from each other in the lengths of the rDNA inserts. Physical maps of these length variants cloned were constructed using EcoRI, SalI, HpaI, MluI and AccI and evidence was obtained that the length heterogeneity was due mainly to the differing number of 325 base pairs (bp) subrepeating elements in the large spacer. Sequence analysis of this subrepeating element revealed that it consisted of a duplet of an approximately 155 bp sequence and a 14 bp unrelated sequence. This structure of the repetitive element is novel.