Abstract
The 5S rRNA genes from 2 species of the Ostreidae family, Crassostrea angulata and Crassostrea gigas, were molecularly characterized. The genes were amplified, cloned, and sequenced. The results revealed a 5S rDNA tandem array with a nucleotide sequence in an inverted position within the nontranscribed spacer region that corresponded to the U2 small nuclear RNA (snRNA) gene. The sequence analysis indicated that both genes could be functionally active. The presence of the microsatellite (CT)n·(GA)n at the 3′ end of both genes and the possible involvement of concerted evolution are discussed.Key words: Crassostrea angulata, Crassostrea gigas, 5S rDNA, U2 snRNA, microsatellite, concerted evolution.