Molecular organization of 5S rDNA in fishes of the genus Brycon

There are few reports on the genomic organization of 5S rDNA in fish specie s. To characterize the 5S rDNA nucleotide sequence and chromosomal localiza tion in the Neotropical fishes of the genus Brycon, 5S rDNA copies from sev en species were generated by PCR. The nucleotide sequences of the coding re gion (5S rRNA gene) and the nontranscribed spacer (NTS) were determined, re vealing that the 5S rRNA genes were highly conserved, while the NTSs were w idely variable among the species analyzed. Moreover, two classes of NTS wer e detected in each species, characterized by base substitutions and inserti ons-deletions. Using fluorescence in situ hybridization (FISH), two 5S rDNA chromosome loci that could be related to the two 5S rDNA NTS classes were observed in at least one of the species studied. 5S rDNA sequencing and chr omosomal localization permitted the characterization of Brycon spp. and sug gest a higher similarity among some of them. The data obtained indicate tha t the 5S rDNA can be an useful genetic marker for species identification an d evolutionary studies.