Certain, rare, mutations in the human gene BRIP1/BACH1/FANCJ cause Fanconi anemia, while others have been linked to familial breast cancer. Reduction of function of the C. elegans ortholog,
dog-1, has been reported to produce a high frequency of small deletions upstream of long poly-guanine (poly G) stretches in the genome (1, 2). Based on the nature of the mutations identified, it has been hypothesized that
dog-1may be required to resolve three dimensional structures such as Guanine quadruplexes (G4) on lagging strand DNA during DNA replication. As most
dog-1deletions have been identified in individual worms by PCR, it is not clear if the full spectrum of mutations induced by
dog-1has been characterized. To test the specificity of
dog-1 for poly G stretches we screened for heritable presenilin suppressor (spr) gene mutations in a
dog-1(
gk10) I;
sel-12(
ty11) X background. Of the seven genes that mutate at high frequency to suppress
sel-12, only one,
spr-3, has a poly G stretch in, or near, the gene. As expected, 12/14 strong spr mutations recovered were small deletions affecting the poly G stretch of
spr-3, indicating that
dog-1 is highly specific for poly G stretches. The mutation frequency at the
spr-3 poly G is 4 X 10 -4, very similar to the EMS frequency for this gene. To determine more completely the range of
dog-1target sequences, we screened for spontaneous mutations with a strong visible phenotype. From analyzing many of these mutants we have found that
dog-1mutations are almost always associated with a putative G4 sequence, however not just poly G but also other G rich sequences can become unstable. These results are a strong confirmation of the original model. The largest class of mutations is small deletions starting at G4 sequences but we have also recovered larger deletions, deletions with insertions and reciprocal translocations at lower frequency. The strong association of
dog-1mutations with G4 sequences helped us to rapidly identify the sites of mutations in many alleles of previously characterized genes and helped us to positionally clone mutations in four genes,
dpy-1,
ngn-1,
nhr-67 and
pptf-1 that had not previously been cloned or recovered in forward genetic screens. Furthermore,
dog-1 induced mutations often have different properties than alleles generated by the knock out consortiums. We are now testing whether we can use comparative genome hybridization (CGH) approaches to systematically detect
dog-1 induced mutations in order to characterize a large collection of
dog-1 induced mutations. 1 Cheung I et al. (2002) Nat. Genet. 31, 405-409. 2 Youds JL, et al. (2006) Genetics 173, 697-708.