The Tofu mutation restores female fertility to Drosophila with a null BEAF mutation.

Compensatory mutations offer clues to deciphering the role of a particular protein in cellular processes. Here we investigate an unknown compensatory mutation, present in the BEAF NP6377 fly line, that provides sufficient rescue of the defective ovary phenotype caused by null BEAF alleles to allow maintenance of fly stocks lacking the chromatin domain insulator proteins Boundary Element-Associated Factors BEAF-32A and BEAF-32B. We call this mutation Tofu . We employ both classical genetics and genomic sequencing to attempt to identify the mutation. We find evidence that points to a mutation in a predicted Polycomb response element upstream of the ribbon gene, which may lead to aberrant rib expression.