In vitro nitrocellulose filter-binding assays confirm the transcription start site as well as indicate H1 as the region essential for Rra-S15 binding. A: Truncation sites and specific mutations to the Rra-RNA. The start codon AUG is boxed, and a red bar is over the ribosome-binding site. B: 5′ truncations; C: 3′ truncations; D: Putative binding-site mutations. Each curve represents at least three independent replicates. For the purposes of comparison, the data from Rra-RNA1 was repeated on graphs B &D. Reported KD measurements represent the protein concentration at which half of the maximum percentage of Rra-RNA is protein bound. Max% refers to the maximum percentage of Rra-RNA that interacts with Rra-S15 in this in vitro assay (see Methods for calculations).