Single-strand DNA-binding protein

Chase, J.W., Merrill, B.M., and Williams, K.P. (1983) F sex factor encodes a single-stranded DNA binding protein (SSB) with extensive sequence homology to Escherichia coli SSB. Proc. Natl. Acad. Sci. USA 80, 5480-5484. 

G. Lindberg, S. C. Kowalczykowski, J. K. Rist, A. Sugino, and L. B. Rothman-Denes, Purification and characterization of the coliphage N4-coded single-stranded DNA binding protein, J. Biol. Chem. 264, 12700-12708 (1989). 

StabiUzation of unwound template strands Single-stranded DNA-binding protein (SSB) Single-stranded DNA-binding protein (SSB)... 

Figure 20.14 Preparation for DNA replication. At Least three proteins are involved DNA helicases disrupt hydrogen bonds between bases to allow the two strands to unwind single-strand DNA-binding proteins stabilise the unbound strands in preparation for base pairings DNA topoisomerase relaxes strain in the strands to facilitate polymerisation.

Bonne, C., Duguet, M., and de Recondo, A.M. (1980) Single-strand DNA binding protein from rat liver interactions with supercoiled DNA. Nucleic Acids Res. 8, 4955-4968. 

Single-stranded DNA binding proteins (SSBs) bind to this short region of ssDNA, which promotes further unwinding of a nearby A+T-rich region. 

Figure 11-2. The prokaryotic DNA replication fork. A schematic representation of semi-conservative replication of DNA by different mechanisms on the leading and lagging strands by DNA polymerase III (DNA pol III) is shown. Other enzymes and accessory proteins that participate in initiation, elongation, and ligation phases of the process are indicated, with DNA pol I depicted as having just dissociated from a completed Okasaki fragment. SSBs, single-stranded DNA binding proteins.

Mismatch repair protein mutL Single-stranded DNA-binding protein ssb DNA repair uvrA Helicase dnaB RNA polymerase frpoB subunits rpoCJ... 

Two other protein complexes also function in eukaryotic DNA replication. RPA (replication protein A) is a eukaryotic single-stranded DNA-binding protein, equivalent in function to the E. coli SSB protein. RFC (replication/actor (J) is a clamp loader for PCNA and facilitates the assembly of active replication complexes. The subunits of the RFC complex have significant sequence similarity to the subunits of the bacterial clamploading (y) complex. 

The process of eukaryotic DNA replication closely follows that of prokaryotic DNA synthesis. Some differences, such as the multiple origins of replication in eukaryotic cells versus single origins of replication in prokaryotes, have already been discussed. Eukaryotic single-stranded DNA-binding proteins and ATP-dependent DNA helicases have been identified, whose functions are analogous to those of the prokaryotic enzymes previously discussed. In contrast, RNA primers are removed by RNase H. 

A group of proteins form the prepriming complex. They recognize the origin of replication (dnaA protein), maintain the separation of the parental strands (single-stranded DNA-binding proteins), and unwind the double helix ahead of the advancing replication fork (helicase). 

Gray, D.M., Gray, C.W., Mou, T.C., and Wen, J.D. 2002. CD of single-stranded, double-stranded, and G-quartet nucleic acids in complexes with a single-stranded DNA-binding protein. Enantiomer 7 49-58. 

Some DNA-binding proteins specifically bind to Z DNA. How could these proteins help stabilize DNA in the Z configuration (Hint How do single-stranded DNA-binding proteins destabilize duplex structures )... 

Replication starts by the separation of the strands of DNA and the formation of a local bubble at a specific DNA site called the origin of replication (ori). A helicase enzyme uses energy from ATP hydrolysis to effect this action. Single-strand DNA binding proteins stabilize the strands during the subsequent steps. The original DNA strands will function as the templates that will direct synthesis of the complementary strands. A nucleotide on the template strand will determine which deoxyribonucleotide (dNTP) will be incorporated in the newly synthesized strand. This replica-... 

Hyland, E.M., Rezende, L.F., and Richardson, C.C. 2003. The DNA binding domain of the gene 2.5 single-stranded DNA-binding protein of bacteriophage T7. J Biol Chem 278(9) 7247-7256. 

These studies [45] [47] suggest that specific protein-protein interactions between a single-stranded-DNA-binding protein and two replicative DNA-helicases allows substantial unwinding of substrates containing the major cisplatin lesion, but the mechanisms of stimulation of the helicases activities by the ICP8 protein appears to be different for the two enzymes. 

Figure 7-14. Example of a fluorescence titration. Intrinsic protein fluorescence is measured in a titration of the E. coli single-strand DNA binding protein to poly-dT. A mixture of protein (at 0.25pM) and DNA was titrated into protein solution (also at 0.25 pM) so that the concen-...

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