Question

Single-stranded DNA (ssDNA) binding proteins (SSBs) are important players in DNA replication because they prevent single-stranded DNA folding in on itself to form intramolecular helices and hairpins. SSBs accomplish this job by which of the following? explain your answer.

1. Recruiting nanoscale sheepdogs to the single-stranded DNA, nipping at the exposed H-bond donors and acceptor groups, herding the ssDNA away from any potential intramolecular interactions.

2. Binding to the backbone of ssDNA, restricting the capacity of ssDNA to curve or twist in order to bind to itself.

3. Binding to the exposed nitrogenous bases of ssDNA, covering them up so they cannot hydrogen bond with other bases and therefore cannot assemble into intramolecular helices.

Answer 1

Single Stranded DNA binding proteins have the property to bind single stranded DNA created by unwinding of doublestranded DNA with the help of helicase. These SSBs bind to backbone of only one strand of DNA (Lagging strand template- 5' -3' strand of original DNA) and prevent the unwound DNA to curve or twist or strand annealing. However in this process studies have revealed that the nitrogenous bases remain exposed when SSBs are bound to DNA strand so that they remain accesible to replication machinery for succesful replication. Therefore option 2 is correct.