sentences:  DNA polymerase δ is able to displace up to 2 to 3 nucleotides of DNA or RNA ahead of its polymerization, generating a short "flap" substrate for Fen1, which can remove nucleotides from the flap, one nucleotide at a time.By repeating cycles of this process, DNA polymerase δ and Fen1 can coordinate the removal of RNA primers and leave a DNA nick at the lagging strand.It has been proposed that this iterative process is preferable to the cell because it is tightly
  regulated and does not generate large flaps that need to be excised.