Structure and Organization of the Engraulidae Family U2 snRNA: An Evolutionary Model Gene?

The U2 snRNA multigene family has been analyzed in four species of the Engraulidae family--Engraulis encrasicolus, Engraulis mordax, Engraulis ringens, and Engraulis japonicas--with the object of understanding more about the structure of this multigene family in these pelagic species and studying their phylogenetic relationships. The results showed that the cluster of this gene family in the Engraulis genus is formed by the U2-U5 snRNA with highly conserved sequences of mini- and micro-satellites, such as (CTGT)n, embedded downstream of the transcription unit; findings indicate that this gene family evolved following the concerted model. The phylogenetic analysis of the non-transcribed spacer of cluster U2-U5 snDNA in the 4 species showed that the sequences of the species E. encrasicolus and E. japonicus are closely related; these two are genetically close to E. mordax and slightly more distant from E. ringens. The data obtained by molecular analysis of U2-U5 snDNA and their secondary structure, with the presence of the micro-satellite (CTGT)n and mini-satellites, show clearly that the species E. encrasicolus and E. japonicus are closely related and would be older than E. mordax and E. ringens.