title: Functions of the ATP hydrolysis subunits (RecB and RecD) in the nuclease reactions catalyzed by the RecBCD enzyme from Escherichia coli.
abstract: The RecBCD enzyme from Escherichia coli is an ATP-dependent nuclease and helicase. Two of its subunits, the RecB and RecD proteins, are DNA-dependent ATPases. We have purified RecB and RecD proteins with mutations in their consensus ATP binding sites to study the functions of these subunits in the ATP-dependent nuclease activities of RecBCD. Reconstituted heterotrimeric enzymes were prepared by mixing wild-type RecB or RecB-K29Q mutant protein (RecB*) with purified RecC protein, and with a histidine-tagged wild-type RecD (hD) or mutant hRecD-K177Q (hD*) protein. RecBCD and all four reconstituted enzymes (wild-type, two single mutants, and the double mutant) cleave a single-stranded DNA oligomer substrate (25-mer) in the absence of ATP at rates of 0.03 to 0.06 min-1. The nuclease reaction catalyzed by RecB*ChD* is not stimulated significantly by ATP, while the reactions catalyzed by RecBCD, RecBChD, RecBChD*, and RecB*ChD are 300 to 3000 fold faster in the presence of 0.5 mM ATP. RecB*ChD* also has very low ATP hydrolysis activity (approximately 10(3)-fold less than RecBCD), as do the individual mutant RecB* and hRecD* proteins (approximately 100-fold less than RecB or hRecD). The products from the ATP-stimulated nuclease reaction with the oligomer substrate suggest a mechanism where two DNA molecules bind to the enzyme in opposite orientations and are cleaved by the nuclease active site. Cleavage towards the 3'-end of one oligomer (observed with RecBChD*) depends on the wild-type RecB subunit, while RecD-dependent cleavage (observed with RecB*ChD) occurs towards the 5'-end of the second bound oligomer.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA.
authors.forename: H W
authors.initials: HW
authors.lastname: Chen
authors.forename: D E
authors.initials: DE
authors.lastname: Randle
authors.forename: M
authors.initials: M
authors.lastname: Gabbidon
authors.forename: D A
authors.initials: DA
authors.lastname: Julin
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D002384:Catalysis; D003067:Coenzymes / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D006868:Hydrolysis; D016296:Mutagenesis; D010957:Plasmids; D013379:Substrate Specificity
chemical_list: D003067:Coenzymes; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D000255:Adenosine Triphosphate; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli; D004265:DNA Helicases