The
him-6 gene is required for meiotic recombination and consequently for the proper segregation of all chromosomes in Caenorhabditis elegans ( Hodgkin et al., Genetics 91, 67-94, 1979).
him-6 encodes a putative recQ type of DNA helicase which shows strong homology to the human BLM (Bloom's Syndrome) gene product. It is also related to the E. coli RecQ helicase, the S. pombe
rqh1+ gene and the S. cervisiae Sgs1 gene. Blooms syndrome (BS) is a rare autosomal recessive disorder characterized by genomic instability. This phenotype is not confined to mitotic cells. Men with BS are sterile and women are subfertile. Furthermore, the BLM protein has been shown to colocalize with RAD51/DMC1 during meiotic prophase (Moens et al., J. Cell Sci. 113, 663-672, 2000). Sequencing the mutant alleles of
him-6 revealed that
e1423 contains a T to A transition, which gives rise to a stop codon in the helicase domain. The mild allele
e1104 shows a G to Q substitution at a conserved position in the helicase domain. Cytological observations of both
him-6(
e1423) and
him-6(
e1104) homozygotes revealed a high frequency of univalents in oocytes at diakinesis, suggesting that the chromosomes fail to undergo crossing-over or pairing. However, at pachytene stage, where they are fully paired in wild type animals, no visible defects were observed in
him-6 mutants. Immunostaining with an antibody raised against the C-terminal part of the protein localized HIM-6 to the germ line nuclei of both hermaphrodite and male. The protein is present in mitotically dividing nuclei and in all subsequent stages of meiotic prophase. In addition, the protein was also detected in all nuclei of the early embryo. The strong meiotic phenotype suggests a role for the HIM-6 protein in the recombination pathway, but it might not be its sole function. We are currently investigating possible interactions of HIM-6 with other proteins.