Abstract
Abstract PriB, a component of replication restart primosome in E. coli, is a protein necessary for replication restart on the collapsed or disintegrated replication fork. PriB is also an important protein for the assembly of primosome onto ΦX174 genome DNA during replication process. Our previous work showed that PriB is structurally similar to the N-terminal DNA-binding domain of E. coli SSB. In order to investigate the single-stranded DNA binding mode of PriB, we have determined the crystal structure of PriB in complex with dT15 and dT30. These two crystals diffracted to 2.8 and 4.0 □ resolution respectively show identical crystal packing and belong to the same orthorhombic space group P212121. The ssDNA bound state of the PriB is similar to that of the apo form, with significant conformational changes only in the Loop regions, especially in the L45 loop. The structure showed that PriB binds ssDNA primarily by electrostatic interactions of positive-charged residues. L45 loop play important roles in mediating the ssDNA binding path. This structure allows us to propose a molecular basis for DNA binding of E. coli primosomal protein PriB, and furthermore, provides an implication for the putative protein interaction surface that may define the role of PriB in the assembly of primosome.