This protein is an initiator of plasmid replication. RepB possesses nicking-closing (topoisomerase I) like activity. It is also able to perform a strand transfer reaction on ssDNA that contains its target. This family also includes RepA which is an E.coli protein involved in plasmid replication. The RepA protein binds to DNA repeats that flank the repA gene [1-3]. These proteins consist of two domains containing a winged helix-turn-helix motif: the N-terminal one, WH1, is involved in the dimerization of RepE and an auxiliary binding to DNA; the C-terminal one, WH2, represented in this entry, is related to a sequence-specific binding to the common 8 bp of the iteron [4,5].

1: Replication and control of circular bacterial plasmids. del Solar G, Giraldo R, Ruiz-Echevarria MJ, Espinosa M, Diaz-Orejas R; Microbiol Mol Biol Rev 1998;62:434-464. PMID:9618448

2: Regulatory interactions between RepA, an essential replication protein, and the DNA repeats of RepFIB from plasmid P307. Spiers AJ, Bhana N, Bergquist PL; J Bacteriol 1993;175:4016-4024. PMID:8320218

3: Twenty years of the pPS10 replicon: insights on the molecular mechanism for the activation of DNA replication in iteron-containing bacterial plasmids. Giraldo R, Fernandez-Tresguerres ME; Plasmid. 2004;52:69-83. PMID:15336485

4: Structural basis for regulation of bifunctional roles in replication initiator protein. Nakamura A, Wada C, Miki K; Proc Natl Acad Sci U S A. 2007;104:18484-18489. PMID:18000058

5: Structural analysis of a replication protein encoded by a plasmid isolated from a multiple sclerosis patient. Kilic T, Popov AN, Burk-Korner A, Koromyslova A, Zur Hausen H, Bund T, Hansman GS; Acta Crystallogr D Struct Biol. 2019;75:498-504. PMID:31063152