Proper chromosome segregation at meiosis I depends on the alignment of homologous chromosomes, the establishment of the synaptonemal complex (SC), and the formation of chiasmata between homologs. Previous studies have demonstrated that HIM-3, a component of the meiotic chromosome core, is required for these processes (Zetka et al. 1999). The him-3(vv6) mutation results in the substitution of a highly conserved residue of the HORMA domain (Couteau et al. 2004), believed to mediate protein-protein interactions (Aravind et al. 1998). HIM-3 levels in him-3(vv6) mutant germ lines appear to be normal and the protein is loaded to the chromosome core. However, him-3(vv6) mutant germ lines exhibit defects in homologue alignment, extensive non-homologous synapsis, and defects in recombination progression, resulting in defects in chiasma formation that lead to a high embryonic lethality (emb) and a high incidence of male (him) phenotype as consequence of chromosome mis-segregation. To identify proteins that interact with HIM-3 or function in the HIM-3 pathway, we performed an EMS-based suppressor screen using the him-3(vv6) allele to isolate candidates that suppress the embryonic lethality characteristic of him-3(vv6). We isolated a strong extragenic suppressor, vv39, which increases chiasma formation on the autosomes. In him-3(vv6); vv39 mutants, successful homologue alignment is stabilized by synapsis and the non-homologous synapsis defect of him-3(vv6) is suppressed. Antibody staining against the SC components SYP-1 and HIM-3 revealed a reduction of synapsed chromosome cores at pachytene. Furthermore, recombination initiation and progression are restored to a wild-type kinetic in the suppressed background. Interestingly, vv39 is also able to suppress the homologue alignment defect associated with the loss of the HIM-3 paralogue HTP-1, which interacts with HIM-3 and is required for the coordination of homologue alignment and synapsis (Couteau et al. 2005; Martinez-Perez et al. 2005). Successful homologue alignment is also stabilized by synapsis in the htp-1(gk174); vv39 double mutants. I hypothesize vv39 is able to rescue the non-homologous synapsis defects in him-3(vv6) and htp-1(gk174) mutants, therefore homologous chromosomes that are aligned undergo homologous synapsis, and early recombination intermediates can be converted into crossovers. I am currently further characterized the meiotic functions of vv39 through RNAi and other biochemical methods. This work is supported by NSERC.