RecQ and RecG helicases have distinct roles in maintaining the stability of polypurine.polypyrimidine sequences.
DNA triplex structures can block the replication fork and result in double-stranded DNA breaks (DSBs). RecQ and RecG helicases may be important for replication of such sequences as RecQ resolves synthetic triplex DNA structures and RecG mediates replication restart by fork regression. Primer extension on an 88 bp triplex-forming polypurine.polypyrimidine (Pu.Py) tract from the PKD1 gene demonstrated that RecQ, but not RecG, facilitated primer extension by T7 DNA polymerase. A high-throughput, dual plasmid screening system using isogenic bacterial lines deficient in RecG, RecQ, or both, revealed that RecQ deficiency increased mutation to sequence flanking this 88 bp tract by eight to ten-fold. Although RecG facilitated small deletions in an 88 bp mirror repeat-containing sequence, it was absolutely required to maintain a 2.5 kb Pu.Py tract containing multiple mirror repeats. These results support a two-tiered model where RecQ facilitates fork progression through triplex-forming tracts and, failing processivity, RecG is critical for replication fork restart.
Dixon
Bradley P
BP
Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, MLC 7022, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, United States.
Lu
Lu
L
Chu
Albert
A
Bissler
John J
JJ
D015153:Blotting, Western; D004247:DNA / Q000737:chemistry*; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000502:physiology*; D007613:Kanamycin Resistance; D009154:Mutation / Q000235:genetics; D009690:Nucleic Acid Conformation; D010957:Plasmids; D011687:Purines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*; D053484:RecQ Helicases / Q000502:physiology*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000378:metabolism
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D011687:Purines; D011743:Pyrimidines; D012097:Repressor Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; C051802:triplex DNA; C071446:RecG protein, E coli; D004247:DNA; D053484:RecQ Helicases