Abstract
We recently demonstrated that the RecBCD enzyme is a bipolar DNA helicase that employs two single-stranded DNA motors of opposite polarity to drive translocation and unwinding of duplex DNA. We hypothesized that this organization may explain the exceptionally high rate and processivity of DNA unwinding catalyzed by the RecBCD enzyme. Using a stopped-flow dye displacement assay for unwinding activity, we test this idea by analyzing mutant RecBCD enzymes in which either of the two helicase motors is inactivated by mutagenesis. Like the wild-type RecBCD enzyme, the two mutant proteins maintain the ability to bind tightly to blunt duplex DNA ends in the absence of ATP. However, the rate of forward translocation for the RecB motor-defective enzyme is only ∼30% of the wild-type rate, whereas for the RecD motor-defective enzyme, it is ∼50%. More significantly, the processivity of translocation is substantially reduced by ∼25- and 6-fold for each mutant enzyme, respectively. Despite retaining the capacity to bind blunt dsDNA, the RecB-mutant enzyme has lost the ability to unwind DNA unless the substrate contains a short 5′-terminated single-stranded DNA overhang. The consequences of this observation for the architecture of the single-stranded DNA motors in the initiation complex are discussed.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 37069-37077 |
| Number of pages | 9 |
| Journal | Journal of Biological Chemistry |
| Volume | 280 |
| Issue number | 44 |
| DOIs | |
| State | Published - Nov 4 2005 |
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ASJC Scopus subject areas
- Biochemistry
Cite this
Bipolar DNA translocation contributes to highly processive DNA unwinding by RecBCD enzyme. / Dillingham, Mark S.; Webb, Martin R.; Kowalczykowski, Stephen C.
In: Journal of Biological Chemistry, Vol. 280, No. 44, 04.11.2005, p. 37069-37077.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Bipolar DNA translocation contributes to highly processive DNA unwinding by RecBCD enzyme
AU - Dillingham, Mark S.
AU - Webb, Martin R.
AU - Kowalczykowski, Stephen C.
PY - 2005/11/4
Y1 - 2005/11/4
N2 - We recently demonstrated that the RecBCD enzyme is a bipolar DNA helicase that employs two single-stranded DNA motors of opposite polarity to drive translocation and unwinding of duplex DNA. We hypothesized that this organization may explain the exceptionally high rate and processivity of DNA unwinding catalyzed by the RecBCD enzyme. Using a stopped-flow dye displacement assay for unwinding activity, we test this idea by analyzing mutant RecBCD enzymes in which either of the two helicase motors is inactivated by mutagenesis. Like the wild-type RecBCD enzyme, the two mutant proteins maintain the ability to bind tightly to blunt duplex DNA ends in the absence of ATP. However, the rate of forward translocation for the RecB motor-defective enzyme is only ∼30% of the wild-type rate, whereas for the RecD motor-defective enzyme, it is ∼50%. More significantly, the processivity of translocation is substantially reduced by ∼25- and 6-fold for each mutant enzyme, respectively. Despite retaining the capacity to bind blunt dsDNA, the RecB-mutant enzyme has lost the ability to unwind DNA unless the substrate contains a short 5′-terminated single-stranded DNA overhang. The consequences of this observation for the architecture of the single-stranded DNA motors in the initiation complex are discussed.
AB - We recently demonstrated that the RecBCD enzyme is a bipolar DNA helicase that employs two single-stranded DNA motors of opposite polarity to drive translocation and unwinding of duplex DNA. We hypothesized that this organization may explain the exceptionally high rate and processivity of DNA unwinding catalyzed by the RecBCD enzyme. Using a stopped-flow dye displacement assay for unwinding activity, we test this idea by analyzing mutant RecBCD enzymes in which either of the two helicase motors is inactivated by mutagenesis. Like the wild-type RecBCD enzyme, the two mutant proteins maintain the ability to bind tightly to blunt duplex DNA ends in the absence of ATP. However, the rate of forward translocation for the RecB motor-defective enzyme is only ∼30% of the wild-type rate, whereas for the RecD motor-defective enzyme, it is ∼50%. More significantly, the processivity of translocation is substantially reduced by ∼25- and 6-fold for each mutant enzyme, respectively. Despite retaining the capacity to bind blunt dsDNA, the RecB-mutant enzyme has lost the ability to unwind DNA unless the substrate contains a short 5′-terminated single-stranded DNA overhang. The consequences of this observation for the architecture of the single-stranded DNA motors in the initiation complex are discussed.
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UR - http://www.scopus.com/inward/citedby.url?scp=27744469165&partnerID=8YFLogxK
U2 - 10.1074/jbc.M505520200
DO - 10.1074/jbc.M505520200
M3 - Article
C2 - 16041061
AN - SCOPUS:27744469165
VL - 280
SP - 37069
EP - 37077
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 44
ER -