The Pu-rich strand of the IVS21 88-bp mirror repeat Pu-Py sequence inhibits primer extension.
A, sequence of the 88-bp PKD1 Pu-Py sequence. Ramped shapes indicate mirror symmetry repeats. B, primer extension. Bovine polymerase α (pol α) was used to extend primers on oligonucleotides containing the IVS21 Pu-rich (R) or Py-rich (Y) template sequence. At physiological pH, replication is inhibited only with the Pu-rich template. Lane 1, marker; lanes 2, 5, and 8, no polymerase; lanes 3 and 4, 6 and 7, and 9 and 10, contain the polypyrimidine (Py-rich) template, the control template (C), and the polypurine (Pu-rich) template at low and high polymerase concentration, respectively. C, interpretation of primer extension results.