Ara-C primer assignment. Shown is the double-stranded DNA segment of human cofilin 1 gene that was used for mutagenesis. Capital letters and arrows represent primers containing Ara-C molecules. Lower case letters represent deleted nucleotides, achieved with primer Ara-C2-A (broken line). Xs in primers denote Ara-C molecules that replace the original deoxy cytidine molecules. Note that the 5' end of primer Ara-C2-A was designed to produce an overhang, that restricts ligation to the 3' segment of the PCR product (see also Fig 2) only if termination occurred after the first Ara-C molecule. The 5' segment of primer Ara-C2-B was designed to produce an overhang that restricts ligation to the 5' segment of the PCR product (see Fig 2) only if termination occurred after two Ara-C molecules. Additionally, two primers containing only one Ara-C molecule insertion were synthesized (not shown).