Organization of the control region. (A) Structure of the control region and its neighbourhood. (B) Shared potential stem-loop structures situated in the highly A+T-biased region on the J-strand (depicted as in S. longifissa). Predicted secondary structures of the first tandem repeat and flanking junctions in S. longifissa (C) and in S. retrolateralis (D). Sl, S. longifissa; Sr, S. retrolateralis. T-stretch is highlighted in carmine. Arrows indicate the initiation location of a certain repeat unit. The numbers of bases between hairpins are shown above the line. Gene lengths are not to scale.