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PcrA, standing for plasmid copy reduced is a helicase that was originally discovered in a screen for chromosomally encoded genes that are affected in plasmid rolling circle replication in the Gram-positive pathogen Staphylococcus aureus.

Biological functions: Genetic and biochemical studies have shown that the helicase is essential for plasmid rolling-circle replication and repair of DNA damage caused by exposure to ultraviolet radiation. It catalyzes the unwinding of double-stranded plasmid DNA that has been nicked at the replication origin by the replication initiation protein. Genetic and biochemical studies have also shown that the helicase plays an important role in cell-survival by regulating the levels of RecA-mediated recombination in Gram-positive bacteria.

Biochemical properties: The helicase is a monomeric translocase and utilizes ATP to unwind DNA. The preferred substrates are single-stranded DNA containing 3' overhangs. The processivity of PcrA is increased in the presence of plasmid replication initiation protein.

Crystal Structure: The structure of the helicase has been solved at high resolution and indicates "inchworming" as the mechanism of translocation on single-stranded DNA. A Mexican-wave model has been proposed based on the changes in conformation of the helicase observed in the product versus substrate complex.

Classification: PcrA belongs to the SF1 superfamily of helicases, which also include the E. coli helicases UvrD and Rep and the eukaryotic helicase Srs2.


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  • Petit, MA; Ehrlich, D (Jun 2002). "Essential bacterial helicases that counteract the toxicity of recombination proteins". EMBO J. 21 (12): 3137–47. doi:10.1093/emboj/cdf317. PMC 126070Freely accessible. PMID 12065426. 
  • Chang, TL; Naqvi, A; Anand, SP; Kramer, MG; Munshi, R; Khan, SA (Nov 2002). "Biochemical characterization of the Staphylococcus aureus PcrA helicase and its role in plasmid rolling circle replication". J Biol Chem. 277 (48): 45880–6. doi:10.1074/jbc.m207383200. 
  • Anand, SP; Zheng, H; Bianco, PR; Leuba, SH; Khan, SA (Jun 2007). "DNA helicase activity of PcrA is not required for the displacement of RecA protein from DNA or inhibition of RecA-mediated strand exchange". J Bacteriol. 189 (12): 4502–9. doi:10.1128/jb.00376-07. 
  • Soultanas, P; Dillingham, MS; Papadopoulos, F; Phillips, SE; Thomas, CD; Wigley, DB (Mar 1999). "Plasmid replication initiator protein RepD increases the processivity of PcrA DNA helicase". Nucleic Acids Res. 27 (6): 1421–8. doi:10.1093/nar/27.6.1421. 
  • Velankar, SS; Soultanas, P; Dillingham, MS; Subramanya, HS; Wigley, DB (Apr 1999). "Crystal structures of complexes of PcrA DNA helicase with a DNA substrate indicate an inchworm mechanism". Cell. 97 (1): 75–84. doi:10.1016/s0092-8674(00)80716-3.