Figure 3.

R-loop formation in (CAG)₇₉·(CTG)₇₉ templates. Templates were in vitro transcribed with T3 and/or T7 RNA polymerases and treated with RNase A (which digests single-stranded RNA) to form each R-loop configuration indicated schematically above the gel. The presence of R-loops forces the plasmid into a more open configuration, thus reducing electrophoretic migration within the gel. Treatment of the R-loop with RNase H cleaves RNA that is base-paired to DNA (the RNA:DNA hybrid) and thus collapses the R-loop, returning DNA to supercoiled form. The position of supercoiled plasmid is indicated as ‘sc’ and open circular plasmid as ‘oc’. Products above these are catenated multimers, which also form R-loops.