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Multiple C-Terminal Tails within a Single E. coli SSB Homotetramer Coordinate DNA Replication and Repair

Antony, Edwin, Weiland, Elizabeth, Yuan, Quan, Manhart, Carol M., Nguyen, Binh, Kozlov, Alexander G., McHenry, Charles S., Lohman, Timothy M.
Journal of Molecular Biology 2013 v.425 pp. 4802-4819
DNA replication, DNA-binding proteins, Escherichia coli, amino acids, genome, metabolism, mutation, single-stranded DNA
Escherichia coli single-stranded DNA binding protein (SSB) plays essential roles in DNA replication, recombination and repair. SSB functions as a homotetramer with each subunit possessing a DNA binding domain (OB-fold) and an intrinsically disordered C-terminus, of which the last nine amino acids provide the site for interaction with at least a dozen other proteins that function in DNA metabolism. To examine how many C-termini are needed for SSB function, we engineered covalently linked forms of SSB that possess only one or two C-termini within a four-OB-fold “tetramer”. Whereas E. coli expressing SSB with only two tails can survive, expression of a single-tailed SSB is dominant lethal. E. coli expressing only the two-tailed SSB recovers faster from exposure to DNA damaging agents but accumulates more mutations. A single-tailed SSB shows defects in coupled leading and lagging strand DNA replication and does not support replication restart in vitro. These deficiencies in vitro provide a plausible explanation for the lethality observed in vivo. These results indicate that a single SSB tetramer must interact simultaneously with multiple protein partners during some essential roles in genome maintenance.