Proposed secondary structures of SDR elements. Loops of elements are given as sequence logos, where the height of the stacked letters at a given position is proportional to the information content at that position and the relative frequency of each nucleotide is given by the relative height of the letter. Consensus nucleotides are represented as either letters or filled circles (A, green; C, blue; G, yellow; T, red). Proposed target sequences are separated from the SDR elements by thick bars. (A–C) Complete SDR elements SDR4, SDR5, and SDR6; (D) variant left loop of SDR4; (E,F) variant right loop of SDR4. The arrows identify an extension of the right stem.