FOKI DNA REPEATS IN THE GENOME OF VICIA-FABA - SPECIES-SPECIFICITY, STRUCTURE, REDUNDANCY MODULATION, AND NUCLEAR-ORGANIZATION

Tandemly repeated DNA sequences about 60 bp in length, which may be is olated by digestion with FokI restriction endonuclease, were studied b y means of molecular and cytological hybridizations in Vicia faba and other Vicia species. The results obtained can be summarized as follows : (i) FokI repeats are almost species specific to V. faba, since they hybridize to a minimum extent to the genomic DNA of only two out of fi ve related species; (ii) these tandemly repeated elements display vari ability in structure even within one and the same array, where differe nt repeats may share not more than 71% homology; (iii) their redundanc y in the genome of V. faba is remarkably high and varies largely betwe en land races (copy numbers per haploid, 1C, genome range from 21.51 x 10(6) to 5.39 x 10(6)); (iv) FokI repeats are clustered in differing amounts in each subtelocentric pair of the chromosome complement and a re missing or present in a nondetectable amount in the submetacentric pair; (vi) chromosome regions that bear these repeats associate closel y to varying degrees in interphase nuclei. These results are discussed in relation to possible functional roles that tandemly repeated DNA s equences such as the FokI elements might play.