Introduction

Eukaryotic DNA replication is a complex process involving multiple specialized enzymes to ensure accurate and efficient genome duplication. Two critical steps in this process are the priming of DNA synthesis and the removal of RNA primers, especially on the lagging strand. These steps are catalyzed by distinct enzymes: DNA polymerase α (Pol α) initiates synthesis by laying down an RNA-DNA primer, and Flap Endonuclease 1 (FEN1) removes RNA primers during Okazaki fragment maturation.

DNA Polymerase α: The Primase and Initiator of DNA Synthesis

• Priming Role: DNA polymerase α is unique among eukaryotic polymerases because it is tightly associated with an RNA primase subunit.

• Primer Synthesis: This complex synthesizes a short RNA primer (~10 nucleotides) followed by a short stretch of DNA (~10-20 nucleotides).

• Initiation of Replication: Pol α initiates DNA synthesis at replication origins and at the start of each Okazaki fragment on the lagging strand.

• Limited Processivity: Pol α has limited ability to elongate DNA, so after primer synthesis, it hands off the growing strand to more processive polymerases (Pol δ for lagging strand, Pol ε for leading strand).

FEN1: The RNA Primer Removal Enzyme

• Function: FEN1 is a structure-specific 5′ flap endonuclease that removes RNA primers by cleaving 5′ flap structures generated during lagging strand synthesis.

• Okazaki Fragment Processing: When DNA polymerase δ displaces the RNA primer of the previous Okazaki fragment, a flap forms which FEN1 cleaves, removing the RNA primer and allowing DNA ligase to seal the nick.

• Coordination: FEN1 works in concert with RNase H and DNA polymerase δ to ensure complete removal of RNA primers and maturation of Okazaki fragments.

Why Other Options Are Incorrect

• PCNA (Proliferating Cell Nuclear Antigen):
  PCNA acts as a sliding clamp that increases the processivity of DNA polymerases δ and ε but does not synthesize primers or remove RNA primers.

• DNA Polymerase δ and ε:
  Pol δ mainly synthesizes the lagging strand after primer synthesis, and Pol ε synthesizes the leading strand. Neither initiates synthesis nor removes RNA primers.

Summary Table

Final Answer

(2) DNA Pol α and FEN1, respectively

Keywords

eukaryotic DNA replication, DNA polymerase α, FEN1, RNA primer removal, Okazaki fragments, lagging strand synthesis, primase activity, flap endonuclease, DNA replication enzymes, DNA polymerase δ, DNA polymerase ε, PCNA

Conclusion

In eukaryotic DNA replication, DNA polymerase α initiates DNA synthesis by synthesizing a short RNA-DNA primer, essential for both leading and lagging strand initiation. The RNA primers laid down on the lagging strand are subsequently removed by FEN1, which cleaves flap structures formed during Okazaki fragment maturation. This coordinated action ensures accurate and efficient DNA replication, maintaining genome integrity.