Elements R1 and R2 are subject to the same recombinational forces that give rise to the concerted evolution of the rDNA units. Molecular phylogenetic analysis of elements from 16 Drosophila species suggests these elements have been stable components of the rDNA locus for the 50-70 million year history of the Drosophila genus.
Analysis of 5' junction sequences of 94 R2-elements from 14 species reveals that no sequences at the 5' end of the R2-element appear to be required for element integration. A model in which the R2-element reverse transcriptase is capable of switching templates from the R2-element RNA transcript to the upstream 28SrRNA gene can best explain the observed 5' junction sequences.
Elements R1 and R2 are subject to the same recombinational forces that give rise to the concerted evolution of the rDNA units. Molecular phylogenetic analysis of elements from 16 Drosophila species suggests these elements have been stable components of the rDNA locus for the 50-70 million year history of the Drosophila genus.
Analysis of 5' junction sequences of 94 R2-elements from 14 species reveals that no sequences at the 5' end of the R2-element appear to be required for element integration. A model in which the R2-element reverse transcriptase is capable of switching templates from the R2-element RNA transcript to the upstream 28SrRNA gene can best explain the observed 5' junction sequences.