title: Induced mutagenesis in Ustilago maydis. I. Isolation and characterization of a radiation-revertible allele of the structural gene for nitrate reductase.
abstract: A UV-revertible mutant of the nar1 structural gene for nitrate reductase was isolated in wild-type (nar+ nir+) Ustilago maydis. It proved to be vigorously revertible by gamma rays as well. Genetic analysis revealed that the strain carried a single, nonleaky, recessive allele (nar1-m) with an unusually high spontaneous reversion rate (approximately 3 X 10(-5)/div.). Reliable reversion frequencies were determined with a special agar medium that reduced the normally high level of residual growth observed on nitrate minimal agar. Radiation-induced reversion frequencies in the homozygous diploid were approximately twice those in the haploid. Following crosses to wild type, two revertants (one spontaneous and one UV-induced) were found to map at nar1. Although the molecular basis of nar1-m reversion is not known, available data suggest that some form of point mutation is involved.
mesh_terms: D000483:Alleles; D001487:Basidiomycota / Q000528:radiation effects*; D005796:Genes; D009154:Mutation; D009565:Nitrate Reductases / Q000378:metabolism*; D011831:Radiation Genetics; D014466:Ultraviolet Rays; D014588:Ustilago / Q000201:enzymology / Q000302:isolation & purification / Q000528:radiation effects*
chemical_list: D009565:Nitrate Reductases