Organization of 5S rDNA in species of the fish Leporinus: two different genomic locations are characterized by distinct nontranscribed spacers

To address understanding the organization of the 5S rRNA multigene family i n the fish genome, the nucleotide sequence and organization array of 5S rDN A were investigated in the genus Leporinus, a representative freshwater fis h group of South American fauna. PCR, subgenomic library screening, genomic blotting, fluorescence in situ hybridization, and DNA sequencing were empl oyed in this study. Two arrays of 5S rDNA were identified for all species i nvestigated, one consisting of monomeric repeat units of around 200 bp and another one with monomers of 900 bp. These 5S rDNA arrays were characterize d by distinct NTS sequences (designated NTS-I and NTS-II for the 200- and 9 00-bp monomers, respectively); however, their coding sequences were nearly identical. The 5S rRNA genes were clustered in two chromosome loci, a major one corresponding to the NTS-I sites and a minor one corresponding to the NTS-II sites. The NTS-I sequence was variable among Leporinus spp., whereas the NTS-II was conserved among them and even in the related genus Schizodo n. The distinct 5S rDNA arrays might characterize two 5S rRNA gene subfamil ies that have been evolving independently in the genome.