Essential to the two distinct cellular events of genetic recombination and SOS induction in Escherichia coli, RecA protein promotes the homologous pairing and exchange of DNA strands and the proteolytic cleavage of the LexA repressor, respectively. Since both of these activities require single-stranded DNA (ssDNA) and ATP, the inter-relationship be...
The double substitution of Glu156 with Leu and Gly157 with Val in the Escherichia coli RecA protein results in a severely reduced level of recombination and constitutive coprotease behavior. Here we present our examination of the biochemical properties of this mutant protein, RecA N99, in an effort to understand its phenotype and the role of loop 1...
The Rad51 nucleoprotein filament mediates DNA strand exchange, a key step of homologous recombination. This activity is stimulated by replication protein A (RPA), but only when RPA is introduced after Rad51 nucleoprotein filament formation. In contrast, RPA inhibits Rad51 nucleoprotein complex formation by prior binding to single-stranded DNA (ssDN...
The mutation of Pro67 to Trp (P67W) in the Escherichia coli RecA protein results in reduced recombination and constitutive coprotease phenotypes. We examined the biochemical properties of this mutant in an effort to understand these altered behaviors. We find that RecA P67W protein can access single-stranded DNA (ssDNA) binding sites within regions...
In the budding yeast Saccharomyces cerevisiae, the RAD52 gene is essential for all homologous recombination events and its homologue, the RAD59 gene, is important for those that occur independently of RAD51. Both Rad52 and Rad59 proteins can anneal complementary single-stranded (ss) DNA. We quantitatively examined the ssDNA annealing activity of Ra...
Double-strand DNA break repair and homologous recombination in Escherichia coli proceed by the RecBCD pathway, which is regulated by cis-acting elements known as chi sites. A crucial feature of this regulation is the RecBCD enzyme-directed loading of RecA protein specifically onto the 3 -terminal, chi-containing DNA strand. Here we show that RecBC ...
E. coli RecQ protein is a multifunctional helicase with homologs that include the S. cerevisiae Sgs1 helicase and the H. sapiens Wrn and Blm helicases. Here we show that RecQ helicase unwinds a covalently closed double-stranded DNA (dsDNA) substrate and that this activity specifically stimulates E. coli topoisomerase III (Topo III) to fully catenat...
The RecBCD enzyme is a complex heterotrimeric helicase/nuclease that initiates recombination at double-stranded DNA breaks. In Escherichia coli, its activities are regulated by the octameric recombination hotspot, χ (5 -GCTGGTGG), which is read as a single-stranded DNA sequence while the enzyme is unwinding DNA at over ∼1,000 bp/s. Previous studies...
Many biologically important proteins bind nonspecifically, and often cooperatively, to single-or double-stranded nucleic acid lattices in discharging their physiological functions. This binding can generally be described in thermodynamic terms by three parameters: n, the binding site size; K, the intrinsic binding constant; omega, the binding coope...
