PcrA

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.

#Iordanescu S. Characterization of the "Staphylococcus aureus" chromosomal gene pcrA, identified by mutations affecting plasmid pT181 replication. Mol Gen Genet. 1993 Oct;241(1-2):185-92.
#Petit MA, Dervyn E, Rose M, Entian KD, McGovern S, Ehrlich SD, Bruand C. PcrA is an essential DNA helicase of Bacillus subtilis fulfilling functions both in repair and rolling-circle replication. Mol Microbiol. 1998 Jul;29(1):261-73.
#Petit MA, Ehrlich D. Essential bacterial helicases that counteract the toxicity of recombination proteins. EMBO J. 2002 Jun 17;21(12):3137-47.

#Chang TL, Naqvi A, Anand SP, Kramer MG, Munshi R, Khan SA. Biochemical characterization of the "Staphylococcus aureus" PcrA helicase and its role in plasmid rolling circle replication. J Biol Chem. 2002 Nov 29;277(48):45880-6. Epub 2002 Sep 19.
#Anand SP, Zheng H, Bianco PR, Leuba SH, Khan SA. 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. 2007 Jun;189(12):4502-9. Epub 2007 Apr 20.
#Soultanas P, Dillingham MS, Papadopoulos F, Phillips SE, Thomas CD, Wigley DB. Plasmid replication initiator protein RepD increases the processivity of PcrA DNA helicase. Nucleic Acids Res. 1999 Mar 15;27(6):1421-8.
#Velankar SS, Soultanas P, Dillingham MS, Subramanya HS, Wigley DB. Crystal structures of complexes of PcrA DNA helicase with a DNA substrate indicate an inchworm mechanism. Cell. 1999 Apr 2;97(1):75-84.