Homologous recombination (HR) serves to eliminate deleterious
lesions, such as double-stranded breaks and interstrand crosslinks,
from chromosomes. HR is also critical for the preservation of replication
forks, for telomere maintenance, and chromosome segregation
in meiosis I. As such, HR is indispensable for the maintenance
of genome integrity and the avoidance of cancers in humans. The
HR reaction is mediated by a conserved class of enzymes termed
Rad51 and disrupted meiotic cDNA1 (Dmc1) are the two eukaryotic DNA
recombinases that participate in homology search and strand exchange
reactions during homologous recombination mediated DNA repair. Rad51
expresses in both mitotic and meiotic tissues whereas Dmc1 is confined to
DNA topoisomerase 6 (TOP6) belongs to a novel family of type II DNA
topoisomerases present, other than in archaebacteria, only in plants. Here
we report the isolation of full-length cDNAs encoding putative TOP6 sub-units A and B from rice (Oryza sativassp.indica), preserving all the struc-tural domains conserved among archaebacterial TOP6 homologs and
eukaryotic meiotic recombination factor SPO11.
The human Rad51 protein, a eukaryotic ortholog of the bacterial RecA
protein, is a key enzyme that functions in homologous recombination and
recombinational repair of double strand breaks. The Rad51 protein con-tains two flexible loops, L1 and L2, which are proposed to be sites for
DNA binding, based on a structural comparison with RecA.
In eukaryotes, meiosis leads to genetically variable gametes through recom-bination between homologous chromosomes of maternal and paternal ori-gin. Chromatin organization following meiotic recombination is critical to
ensure the correct segregation of homologous chromosomes into gametes.
However, the mechanism of chromatin organization after meiotic recombi-nation is unknown.