CHARACTERIZATION OF REPETITIVE DNA-SEQUENCES CARRYING 5S RDNA OF THE TRIPLOID GINBUNA (JAPANESE SILVER CRUCIAN CARP, CARASSIUS-AURATUS LANGSDORFI)

Repetitive DNA sequences (Hi-b; 209 bp in length) were isolated from t he HindIII digests of the genomic DNA of the triploid ginbuna, Carassi us auratus langsdorfi. Sequence analyses revealed that the Hi-b repeti tive units were comprised of the complete coding regions of 5S rDNA (1 20 bp in size) and their 5' flanking regions. The sequences of the Hi- b units from the same individual were highly homogeneous. Southern blo t hybridization to the Hi-b probe displayed intricate patterns that re presented the presence of other repetitive units containing the Hi-b r elated sequences. A major family of repetitive sequences related to th e Hi-b was then obtained by the polymerase chain reaction using asymme try primers for the 5S coding regions. These 331-bp sequences (AZ5S's) contained 5S pseudogenes as well as the almost entire Hi-b sequences, and seemed to be the true 5S rDNAs. The tandem arrangements of the AZ 5S sequences explained most of the complex results of Southern blots. Another class of intriguing repeat units (Hi-b-beta and Hi-b-gamma) we re also isolated. Fluorescence in situ hybridization data revealed two major signals on a pair of homologous chromosomes and several minor s ignals on other chromosomes in the triploid ginbuna, indicating the ex istence of the 5S related sequences as several separate clusters. The major spots were shared with the tetraploid ginbuna and goldfish, but not with the diploid ginbuna. When the genomic organization of the Hi- b related sequences in other cyprinid fishes was examined, the hybridi zation patterns of the ginbuna were very simillar to those of the gold fish, but were clearly different from those of the gengorobuna. The ca rp genome showed less complex patterns. Thus, the present 5S rDNA-rela ted sequences could be candidates for phylogenetic molecular markers f or the crucian carp.