DNA Structure and Replication · USMLE Step 1

What is the role of single-stranded DNA binding proteins (SSBs) during replication?

  1. They synthesize the RNA primers used by polymerase
  2. They prevent re-annealing of unwound parental strands
  3. They remove RNA primers from the lagging strand
  4. They seal the nicks left in the sugar-phosphate backbone
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Correct answer: They prevent re-annealing of unwound parental strands

SSBs coat the separated single strands at the replication fork, preventing them from re-forming a double helix or forming secondary structures, thus enabling polymerases to access the templates.

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