Structural evolution of the Drosophila 5S ribosomal genes.

We compare the 5S gene structure from nine Drosophila species. New sequence data (5S genes of D. melanogaster, D. mauritiana, D. sechellia, D. yakuba, D. erecta, D. orena, and D. takahashii) and already-published data (5S genes of D. melanogaster, D. simulans, and D. teissieri) are used in these comparisons. We show that four regions within the Drosophila 5S genes display distinct rates of evolution: the coding region (120 bp), the 5'-flanking region (54-55 bp), the 3'-flanking region (21-22 bp), and the internal spacer (149-206 bp). Intra- and interspecific heterogeneity is due mainly to insertions and deletions of 6-17-bp oligomers. These small rearrangements could be generated by fork slippages during replication and could produce rapid sequence divergence in a limited number of steps.