title: An unstable nuclear gene in phycomyces.
abstract: A gentic instability in Phycomyces is described that appears to be associated with a single nuclear gene, dar. The wild type is able to take up riboflavin and its toxic analogue, deaza-riboflavin, from nanomolar concentrations in the medium. The mutants are unable to take up riboflavin and are resistant to deaza-riboflavin. Forward and reverse mutation rates are estimated to be 4 x 10(-5) and 2 x 10(-3) per nuclear division. Independently arisen dar mutants do not complement in heterokaryons. The mutant alleles are almost completely recessive. The phenotype of spores is not determined cell-autonomously, but is strongly influenced by the allele ratio among the nuclei in the sporangium of origin.
authors.affiliation: Division of Biology, California Institute of Technology, Pasadena, California 91125.
authors.forename: M
authors.initials: M
authors.lastname: Delbrück
authors.forename: T
authors.initials: T
authors.lastname: Ootaki