Evolution of 5S rRNA gene families in Drosophila

In Drosophila virilis, the three clusters of 5S rRNA genes on chromosome 5 comprise two different gene families (B and C), which differ profoundly in the organization of their spacer sequences. While C-type genes, which are found in two of the clusters, exhibit a true repetitive character, the B-type genes of the third cluster are each embedded in completely different genomic environments. Southern blots of genomic DNA of different D. virilis subspecies, D. hydei and D. melanogaster probed with 5S rRNA gene spacer and coding sequences demonstrate the specificity of C-type sequences for the D. virilis species group. The comparative analysis of flanking sequences of 5S rRNA genes of D. virilis, members of the D. melanogaster species subgroup and of the blowfly Calliphora erythrocephala reveals the existence of conserved sequence motifs both in the 5' upstream and 3' downstream flanking regions. Their possible roles in the control of expression and processing of the 5S rRNA precursor molecule are discussed.