The following text describes a protein:
Function:
A helicase/nuclease that prepares dsDNA breaks (DSB) for recombinational DNA repair. Binds to DSBs and unwinds DNA via a rapid (>1 kb/second) and highly processive (>30 kb) ATP-dependent bidirectional helicase. Unwinds dsDNA until it encounters a Chi (crossover hotspot instigator, 5'-GCTGGTGG-3') sequence from the 3' direction. Cuts ssDNA a few nucleotides 3' to Chi site, by nicking one strand or switching the strand degraded (depending on the reaction conditions). The properties and activities of the enzyme are changed at Chi. The Chi-altered holoenzyme produces a long 3'-ssDNA overhang which facilitates RecA-binding to the ssDNA for homologous DNA recombination and repair. Holoenzyme degrades any linearized DNA that is unable to undergo homologous recombination. In the holoenzyme this subunit contributes ATPase, 3'-5' helicase, exonuclease activity and loads RecA onto ssDNA. The RecBC complex requires the RecD subunit for nuclease activity, but can translocate along ssDNA in both directions. The RecBCD complex does not unwind G-quadruplex DNA. Probably interacts with a component of retron Ec48 which moniters RecBCD stability; when RecB is missing or impaired the retron is activated and becomes toxic (Probable).
Miscellaneous:
MISCELLANEOUS: In the RecBCD complex, RecB has a slow 3'-5' helicase, an exonuclease activity and loads RecA onto ssDNA, RecD has a fast 5'-3' helicase activity while RecC stimulates the ATPase and processivity of the RecB helicase and contributes to recognition of the Chi site.
Domain:
The N-terminal DNA-binding domain (residues 1-929) is a ssDNA-dependent ATPase and has ATP-dependent 3'-5' helicase function; both are stimulated in the presence of RecC, suggesting this domain interacts with RecC. Holoenzyme reconstituted with this RecB N-terminal fragment has no nuclease activity. The C-terminal domain (residues 928-1180) has weak ssDNA endonuclease activity as an isolated fragment. RecD probably interacts with this domain. The C-terminal domain interacts with RecA, facilitating its loading onto ssDNA. Interaction is decreased by ATP. The RecB helicase domains change conformation upon nucleotide binding. As ssDNA is unwound and fed to the RecD subunit the latter transmits conformational changes through each subunit to activate the RecB nuclease; The holoenzyme may undergo conformational shifts upon DNA binding: the nuclease domain of RecB may swing away from the DNA exit tunnel in RecC. When Chi DNA binds to the RecC tunnel, the nuclease domain may then swing back to its original position (that seen in crystal structures), allowing it to nick the DNA 3' of the Chi site and then rotate to load RecA. At high Mg(2+) the nuclease domain may swing back more frequently, explaining differences seen in assays performed at high Mg(2+).
Sequence:
MSDVAETLDPLRLPLQGERLIEASAGTGKTFTIAALYLRLLLGLGGSAAFPRPLTVEELLVVTFTEAATAELRGRIRSNIHELRIACLRETTDNPLYERLLEEIDDKAQAAQWLLLAERQMDEAAVFTIHGFCQRMLNLNAFESGMLFEQQLIEDESLLRYQACADFWRRHCYPLPREIAQVVFETWKGPQALLRDINRYLQGEAPVIKAPPPDDETLASRHAQIVARIDTVKQQWRDAVGELDALIESSGIDRRKFNRSNQAKWIDKISAWAEEETNSYQLPESLEKFSQRFLEDRTKAGGETPRHPLFEAIDQLLAEPLSIRDLVITRALAEIRETVAREKRRRGELGFDDMLSRLDSALRSESGEVLAAAIRTRFPVAMIDEFQDTDPQQYRIFRRIWHHQPETALLLIGDPKQAIYAFRGADIFTYMKARSEVHAHYTLDTNWRSAPGMVNSVNKLFSQTDDAFMFREIPFIPVKSAGKNQALRFVFKGETQPAMKMWLMEGESCGVGDYQSTMAQVCAAQIRDWLQAGQRGEALLMNGDDARPVRASDISVLVRSRQEAAQVRDALTLLEIPSVYLSNRDSVFETLEAQEMLWLLQAVMTPERENTLRSALATSMMGLNALDIETLNNDEHAWDVVVEEFDGYRQIWRKRGVMPMLRALMSARNIAENLLATAGGERRLTDILHISELLQEAGTQLESEHALVRWLSQHILEPDSNASSQQMRLESDKHLVQIVTIHKSKGLEYPLVWLPFITNFRVQEQAFYHDRHSFEAVLDLNAAPESVDLAEAERLAEDLRLLYVALTRSVWHCSLGVAPLVRRRGDKKGDTDVHQSALGRLLQKGEPQDAAGLRTCIEALCDDDIAWQTAQTGDNQPWQVNDVSTAELNAKTLQRLPGDNWRVTSYSGLQQRGHGIAQDLMPRLDVDAAGVASVVEEPTLTPHQFPRGASPGTFLHSLFEDLDFTQPVDPNWVREKLELGGFESQWEPVLTEWITAVLQAPLNETGVSLSQLSARNKQVEMEFYLPISEPLIASQLDTLIRQFDPLSAGCPPLEFMQVRGMLKGFIDLVFRHEGRYYLLDYKSNWLGEDSSAYTQQAMAAAMQAHRYDLQYQLYTLALHRYLRHRIADYDYEHHFGGVIYLFLRGVDKEHPQQGIYTTRPNAGLIALMDEMFAGMTLEEA