A tandemly repetitive centromeric DNA sequence of the fish Hoplias malabaricus (Characiformes: Erythrinidae) is derived from 5S rDNA Cesar Martins 1 , Irani Alves Ferreira 1 , Claudio Oliveira 1 , Fausto Foresti 1 & Pedro Manoel Galetti Jr 2 1 Departamento de Morfologia, UNESP-Universidade Estadual Paulista, Instituto de Biocieˆncias, CEP 18618- 000, Botucatu, SP, Brazil (E-mail: cmartins@ibb.unesp.br; Phone/Fax: +55-14-38116264); 2 Departamento de Gene´tica e Evoluc ¸a ˜o, Universidade Federal de Sa ˜o Carlos, Centro de Cieˆncias Biolo ´gicas e da Sau ´de, CEP 13565-905, Sa ˜o Carlos, SP, Brazil Received 15 June 2005; Accepted 31 August 2005 Key words: 5S rDNA, 5S rDNA variant, centromeric DNA, fish, Hoplias malabaricus, satellite DNA Abstract A substantial fraction of the eukaryotic genome consists of repetitive DNA sequences that include satellites, minisatellites, microsatellites, and transposable elements. Although extensively studied for the past three decades, the molecular forces that generate, propagate and maintain repetitive DNAs in the genomes are still discussed. To further understand the dynamics and the mechanisms of evolution of repetitive DNAs in vertebrate genome, we searched for repetitive sequences in the genome of the fish species Hoplias mala- baricus. A satellite sequence, named 5SHindIII-DNA, which has a conspicuous similarity with 5S rRNA genes and spacers was identified. FISH experiments showed that the 5S rRNA bona fide gene repeats were clustered in the interstitial position of two chromosome pairs of H. malabaricus, while the satellite 5SHindIII-DNA sequences were clustered in the centromeric position in nine chromosome pairs of the species. The presence of the 5SHindIII-DNA sequences in the centromeres of several chromosomes indi- cates that this satellite family probably escaped from the selective pressure that maintains the structure and organization of the 5S rDNA repeats and become disperse into the genome. Although it is not feasible to explain how this sequence has been maintained in the centromeric regions, it is possible to hypothesize that it may be involved in some structural or functional role of the centromere organization. Introduction An interesting feature of eukaryote genome is the presence of a substantial fraction of duplicated DNA sequences, most of them composed by non- coding sequences that include satellite, minisatel- lite and microsatellite sequences, and transposable elements. Although studied extensively for the past three decades, the molecular forces that propagate and maintain repetitive DNAs in the genome are still discussed. Among whole sequenced genomes the repetitive areas remains as gaps because of the difficulty in their correct positioning and array in the genome. However, the role of these DNAs in genome organization and evolution, and their impact on speciation has been frequently reported (Charlesworth, Snlegowski and Stephan, 1994). The variation in genome size of different eukary- otes is often reported to differences in the amount of repeated DNA sequences (Cavalier-Smith, 1985; Brenner et al., 1993). Recently advances on studies concerning non-coding repetitive DNA sequences have shown that such sequences are extremely important in the structural and func- tional organization of the genome. Among vertebrate species, studies about repeti- tive sequences have been mainly directed to the understanding of the structure and organization of satellite DNA and ribosomal DNA (rDNA) repeats. Satellite DNA families can correspond to Genetica (2006) 127:133–141 Ó Springer 2006 DOI 10.1007/s10709-005-2674-y