ALTERATION BY SITE-DIRECTED MUTAGENESIS OF THE CONSERVED LYSINE RESIDUE IN THE ATP-BINDING CONSENSUS SEQUENCE OF THE RECD SUBUNIT OF THE ESCHERICHIA-COLI RECBCD ENZYME

The RecD subunit of the RecBCD enzyme from Escherichia coli contains an amino acid sequence common to many enzymes which bind ATP or GTP (Gly-X-X-Gly-X-Gly-Lys-Thr). We have changed the conserved lysine residue (amino acid number 177) in the RecD protein to glutamine to investigate the role of RecD, and ATP-binding to RecD, in the enzymatic activities of RecBCD. The mutant RecD protein assembles with the RecB and RecC subunits and the mutant enzyme, designated RecBCD-K177Q, can be purified in the same way as the wild-type RecBCD enzyme. The mutant RecD subunit in RecBCD-K177Q is photolabeled to a lesser extent by the ATP analogue 8-azido-adenosine-5'-triphosphate than is the wild-type RecD subunit in RecBCD, suggesting that the mutation has reduced the affinity of RecD for ATP.