MODELING THE SECONDARY STRUCTURES OF SLIPPAGE-PRONE HYPERVARIABLE RNAREGIONS - THE EXAMPLE OF THE TIGER BEETLE 18S RIBOSOMAL-RNA VARIABLE REGION V4

Variable regions within ribosomal RNAs frequently vary in length as a result of incorporating products of slippage. This makes constructing secondary-structure models problematic because base homology is diffic ult or impossible to establish between species. Here, we model such a region by comparing the results of the MFOLD suboptimal folding algori thm for different species to identify conserved structures. Based on t he reconstruction of base change on a phylogenetic tree of the species and comparison against null models of character change, we devise a s tatistical analysis to assess support of these structures from compens atory and semi-compensatory (i.e. G.C to G.U or A.U to G.U) mutations. As a model system we have used variable region V4 from cicindelid (ti ger beetle) small subunit ribosomal RNAs (SSU rRNAs). This consists of a mixture of conserved and highly variable subregions and has been su bject to extensive comparative analysis in the past. The model that re sults is similar to a previously described model of this variable regi on derived from a different set of species and contains a novel struct ure in the central, highly variable part. The method we describe may b e useful in modelling other RNA regions that are subject to slippage.