title: Differential chromosomal and mitochondrial DNA synthesis in temperature-sensitive mutants of Ustilago maydis.
abstract: The amount and type of residual DNA synthesis was determined in eight temperature-sensitive mutants of the smut fungus Ustilago maydis after incubation at the restrictive temperature (32 degrees C) for eight hours. Mutants ts-220, ts-207, ts-432 and ts-346 were found to have an overall reduction in the synthesis of both nuclear and mitochondrial DNA comparison to the wild-type. In mutants ts-20, tsd 1-1, ts-84 and pol 1-1 nuclear DNA synthesis was depressed relative to mitochondrial synthesis. The DNA-polymerase mutant pol 1-1 had persistent nuclear synthesis at about 50% of the rate of synthesis of mitochondrial DNA and similar behavior was observed in a diploid homozygous strain. Mutant ts-84 had an initial burst of DNA synthesis which was reduced for nuclear but not mitochondrial synthesis after three hours preincubation at 32 degrees C. tsd 1-1 and ts-20 had nuclear residual synthesis amounting to about 25% of the relative rate of mitochondrial synthesis which correlates to increasing UV sensitivity of these strains on incubation at 32 degrees C. A pol 1-1 ts-84 double mutant had an additive loss of nuclear DNA synthesis which indicates that the steps of replication involved may be sequential.
mesh_terms: D001487:Basidiomycota / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis*; D004272:DNA, Mitochondrial / Q000096:biosynthesis*; D005796:Genes; D009154:Mutation; D013696:Temperature; D014588:Ustilago / Q000378:metabolism*
chemical_list: D004272:DNA, Mitochondrial; D004247:DNA