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Functional complementation of UvsX and UvsY mutations in the mediation of T4 homologous recombination

Farb, Joshua N., Morrical, Scott W.
Nucleic acids research 2009 v.37 no.7 pp. 2336-2345
adenosinetriphosphatase, bacteriophages, homologous recombination, mutants, mutation, proteins, single-stranded DNA
Bacteriophage T4 homologous recombination events are promoted by presynaptic filaments of UvsX recombinase bound to single-stranded DNA (ssDNA). UvsY, the phage recombination mediator protein, promotes filament assembly in a concentration-dependent manner, stimulating UvsX at stoichiometric concentrations but inhibiting at higher concentrations. Recent work demonstrated that UvsX-H195Q/A mutants exhibit decreased ssDNA-binding affinity and altered enzymatic properties. Here, we show that unlike wild-type UvsX, the ssDNA-dependent ATPase activities of UvsX-H195Q/A are strongly inhibited by both low and high concentrations of UvsY protein. This inhibition is partially relieved by UvsY mutants with decreased ssDNA-binding affinity. The UvsX-H195Q mutant retains weak DNA strand exchange activity that is inhibited by wild-type UvsY, but stimulated by ssDNA-binding compromised UvsY mutants. These and other results support a mechanism in which the formation of competent presynaptic filaments requires a hand-off of ssDNA from UvsY to UvsX, with the efficiency of the hand-off controlled by the relative ssDNA-binding affinities of the two proteins. Other results suggest that UvsY acts as a nucleotide exchange factor for UvsX, enhancing filament stability by increasing the lifetime of the high-affinity, ATP-bound form of the enzyme. Our findings reveal new details of the UvsX/UvsY relationship in T4 recombination, which may have parallels in other recombinase/mediator systems.