Three new satellite sequences and a mobile element found inside HSP70 introns of the Mediterranean mussel (Mytilus galloprovincialis)

We report the characterization of 3 new repetitive sequences from the bivalve mollusc Mytilus galloprovincialis, designated Mg1, Mg2, and Mg3, with monomer lengths of 169, 260, and 70 bp, respectively. The 3 repeats together constitute approximately 7.8% of the M. galloprovincialis genome and were found, together with Apal-type 2 repeats, inside the introns of 2 genes of the HSP70 family, hsc70 and hsc71. Both the monomer length and the genomic content of the repeats indicate satellite sequences. The Mg1 repetitive region and its flanking sequences exhibit significant homology to CvE, a member of the Pearl family of mobile elements found in the eastern oyster (Crassostrea virginica). Thus, the whole homologous region is designated MgE, the first putative transposable element characterized in M. galloprovincialis. The Apa1, Mg2, and Mg3 repeats are continuously arranged inside the introns of both the hsc70 and hsc71 genes. The presence of perfect inverted repeats flanking the Apa1-Mg2-Mg3 repetitive region, as well as a sequence analysis of the repeats, indicates a transposition-like insertion of this region. The genes of the HSP70 family are highly conserved, and the presence of repetitive DNA or of mobile elements inside their introns is reported here for the first time.