Open AccessTemplate disruptions and failure of double Holliday junction dissolution during double-strand break repair in Drosophila BLM mutants
Author(s) -
Dena M. Johnson-Schlitz,
William R. Engels
Publication year - 2006
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0607904103
Subject(s) - holliday junction , homologous recombination , rad51 , biology , postreplication repair , dna repair , genetics , mutant , branch migration , gene , microbiology and biotechnology , dna mismatch repair
Previous biochemical studies of theBLM gene product have shown its ability in conjunction with topoisomerase IIIα to resolve double Holliday structures through a process called “dissolution.” This process could prevent crossing over during repair of double-strand breaks. We report an analysis of theDrosophila BLM gene,DmBlm , in the repair of double-strand breaks in the premeiotic germ line ofDrosophila males. With a repair reporter construct, Rr3, and other genetic tools, we show thatDmBlm mutants are defective for homologous repair but show a compensating increase in single-strand annealing. Increases of 40- to 50-fold in crossing over and flanking deletions also were seen. Perhaps most significantly, the template used for homologous repair inDmBlm mutants is itself subject to deletions and complex rearrangements. These template disruptions are indicative of failure to resolve double Holliday junctions. These findings, along with the demonstration that a weak allele of topoisomerase IIIα has some of the same defects asDmBlm , support the dissolution model. Finally, an analysis ofDmBlm mutants in conjunction withmus81 orspnA (Rad51 ) reveals a second function ofBLM distinct from the repair of induced double-strand breaks and possibly related to maintenance of replication forks.