Practice question

DNA polymerases are unable to initiate strand synthesis de novo, requiring pre-existing hydroxyl to elongate. Primase, specialized RNA polymerase subunit of Pol α-primase complex in eukaryotes and DnaG in bacteria, synthesizes short 8-12 nucleotide RNA primer complementary to ssDNA template, providing 3' OH substrate. RNA primer is later removed by RNase H and FEN1 and replaced by DNA via Pol δ during lagging strand maturation. Use of RNA allows marking of nascent fragments and distinction from bulk DNA for removal, prevents errors from ab initio DNA synthesis and ensures strand identity. Leading strand also requires priming at origin.