Binding and melting of D-loops by the Bloom syndrome helicase.
Bloom syndrome is a rare autosomal disorder characterized by predisposition to cancer and genomic instability. BLM, the structural gene mutated in individuals with the disorder, encodes a DNA helicase belonging to the RecQ family of helicases. These helicases have been established to serve roles in both promoting and preventing recombination. Mounting evidence has implicated a function for BLM during DNA replication; specifically, BLM might be involved in rescuing stalled or collapsed replication forks by a recombination-based mechanism. We have tested this idea by examining the binding and melting activity of BLM on oligonucleotide substrates containing D-loops, DNA structures that model the presumed initial intermediate formed during homologous recombination. We find that BLM preferentially melts those D-loops that are formed more favorably by the strand exchange protein Rad51, but whose polarity could be less favorable for enabling restoration of an active replication fork. We propose a model in which BLM selectively dissociates recombination intermediates likely to be unfavorable for recombination-promoted replication.
van Brabant
A J
AJ
Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Ye
T
T
Sanz
M
M
German III
J L
JL
Ellis
N A
NA
Holloman
W K
WK
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D001816:Bloom Syndrome / Q000201:enzymology* / Q000235:genetics*; D004249:DNA Damage; D004265:DNA Helicases / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000378:metabolism; D011485:Protein Binding; D051135:Rad51 Recombinase; D053484:RecQ Helicases; D011995:Recombination, Genetic; D013379:Substrate Specificity
D004268:DNA-Binding Proteins; D009692:Nucleic Acid Heteroduplexes; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases