A variegated position effect inAspergillus nidulans

Abstract

SUMMARY: In mutants at the ‘bristle’ locus ofAspergillus nidulansthe conidiophore remains as a stiff hypha rather than developing a vesicle, sterigmata and conidia. ThebrlA12 allele of this locus has a variegated phenotype, and genetic analysis has shown that this is associated with a translocation which has a breakpoint in the map interval adjacent to thebristlelocus.The mutant phenotype is partially repaired on high-salt medium at low pH, and can also be repaired by suppressors, one of which has been mapped at a locus unlinked tobrlA12.The mutant provides proof that variegation is due to instability of gene expression and not to mutability sincebrlA12 is genetically stable and can be propagated from either conidia or sterile conidiophores, the structures formed at the two extremes of variegation, and the resulting colonies in both cases are identical to the original strain.It has been shown by mitotic recombination that the translocation associated with the variegated mutant is a ‘simple translocation’ in which the distal half of linkage group VIII is attached to the end of linkage group III. This terminal attachment site does not appear to be damaged in any genetically detectable way.