What is the role of SSB proteins?

• A. SSB enzymes ligate Okazaki fragments.
• B. SSB stabilize exposed single-stranded DNA at the replication fork to prevent reannealing and degradation.
• C. SSB are helicases that unwind DNA ahead of the fork.
• D. SSB synthesize RNA primers.

Answer: (B)

Single-stranded DNA binding proteins stabilize exposed single-stranded DNA at the replication fork to prevent reannealing and degradation. When helicase unwinds the DNA, the two strands become ssDNA templates that must stay accessible for synthesis. SSBs quickly bind these regions, keeping them from pairing back up and shielding them from nucleases. This protection keeps the template available for DNA polymerases and helps coordinate fork progression, especially on the lagging strand where many short segments are synthesized. They don’t ligate fragments, unwind DNA, or synthesize RNA primers—that work is done by ligase, helicase, and primase, respectively—while SSBs focus on preserving and stabilizing the single-stranded templates.