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.
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.