Caenorhabditis elegans Genome sequencing

During the first meiotic division, crossovers (COs) between homologous chromosomesensure their correct segregation. COs are produced by homologous recombination(HR) mediated repair of programmed DNA double strand breaks (DSBs). As moreDSBs are induced than COs, mechanisms are required to establish a regulatednumber of COs and to repair remaining intermediates as non-crossovers (NCOs). Weshow that the Caenorhabditis elegans RMI homolog RMH-1 functions during meiosis topromote both CO and NCO HR at appropriate chromosomal sites. RMH-1 accumulatesat CO sites, dependent on known pro-CO factors, and acts to promote CO designationand enforce the CO outcome of HR-intermediate resolution. RMH-1 also localizes atNCO sites and functions in parallel with SMC-5 to antagonize excess HR-basedconnections between chromosomes. Moreover, RMH-1 also has a major role inchanneling DSBs into a NCO HR outcome near the centers of chromosomes, therebyensuring that COs form predominantly at off-center positions.