The
rad-54.L
(me139) mutation was isolated in a modified version of the previously-described Green Eggs & Him EMS screen for meiotic mutants based on mis-segregation of X chromosomes (Kelly et al. 2000). The causative mutation was mapped to chromosome I by outcrossing with worms carrying the tmC18 balancer chromosome (marked with the red pharynx marker tmIs1236 (Dejima et al. 2018)). Homozygous
me139 mutant worms exhibit a variable number of DAPI-stained bodies in diakinesis oocytes and produce many inviable embryos (maternal-effect lethal or Mel phenotype), but they also produce some viable progeny that survive to adulthood (15.2% survivors, n = 961), many of which are males (16% males, n = 146; the high incidence of males or Him phenotype). Three-factor mapping of the Him/Mel phenotype using
dpy-5 and
unc-29 markers indicated a map position near or to the right of
unc-29 (11/11 Dpy non-Unc recombinants picked up the Him/Mel mutation; 7/7 Unc non-Dpy recombinants did not). Consistent with this mapping, whole genome sequencing of DNA from pooled homozygous mutant recombinants revealed a candidate deletion in the
rad-54.L gene (formerly called
rad-54 (Mets and Meyer 2009)). This deletion was confirmed by PCR and Sanger sequencing, which identified the lesion as a 102 nt deletion that removes nucleotide residues I..9065146 - I..9065247, thereby truncating the first coding exon and eliminating the adjacent splice donor sequence and a portion of the adjacent intron. Finally,
rad-54.L
(me139) was confirmed to be the causative mutation based on failure to complement the Mel phenotype of
rad-54.L
(me98), a
rad-54.L null allele (Roelens et al. 2019), as no viable progeny resulted from the embryos produced by
me139 /
me98 heterozygous hermaphrodites. As worms homozygous for the
rad-54L null allele produce 100% dead embryos (Roelens et al. 2019), we infer that
rad-54.L
(me139) does not eliminate RAD-54.L function but instead results in a partial loss of function. Perusal of the mutant sequence indicates a capacity to produce several potential modified versions of the RAD-54.L protein that could retain partial function. For example, there are several potential cryptic splice donor sequences that could be used to generate in-frame translatable mRNAs encoding proteins missing only amino acids 21-35 of the normal RAD-54.L protein (with 43, 60, or 62 extra amino acids inserted). As the affected portion of the protein is N-terminal to the highly conserved ATP binding and enzymatic domains that define the protein superfamily, it is plausible that such altered proteins could be at least partially functional. This partial loss of function allele could prove useful for investigating mechanisms of meiotic chromosome inheritance.