RESUMO
The cyt-12-12 mutant of Neurospora crassa is characterized by slow growth and a deficiency of spectrophotometrically-detectable cytochromes aa3 and c. Using a sib-selection procedure we have isolated the cyt-12+ allele from a cosmid library of N. crassa genomic DNA. Characterization of the cyt-12+ allele reveals that it encodes the structural gene for cytochrome c. DNA sequence analysis of the cyt-12-12 allele revealed a mutation in the cytochrome c coding sequence that results in replacement of a glycine residue, which is invariant in the cytochrome c of other species, with an aspartic acid. Genetic analysis confirms that cyt-12-12 is allelic with the previously-characterized cyc-1-1 mutant, which was also shown to affect the single locus encoding cytochrome c in N. crassa. We suggest that the amount of functional cytochrome c present in mitochondria influences the level of cytochrome aa3.
Assuntos
Grupo dos Citocromos c/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , Genes Fúngicos , Mutação , Neurospora crassa/genética , Alelos , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , Grupo dos Citocromos c/metabolismo , DNA Fúngico/genética , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Humanos , Mitocôndrias/metabolismo , Dados de Sequência Molecular , Neurospora crassa/crescimento & desenvolvimento , Neurospora crassa/metabolismo , Fenótipo , Homologia de Sequência de AminoácidosRESUMO
More than 20 new bacteriophage T4 DNA polymerase mutants have been isolated by a procedure designed to select mutants with high spontaneous mutation rates. Some of the mutants produce the highest mutation frequencies that have been observed in T4 thus far. The design of the selection procedure allows for the isolation of mutator mutants that preferentially induce certain types of replication errors, and some of the mutator mutants have mutational specificities different from wild-type. The new mutants are clustered at just two sites in the DNA polymerase gene, and this result confirms an earlier observation.
Assuntos
DNA Polimerase Dirigida por DNA/genética , Mutação , Fagos T/genética , Replicação do DNA , DNA Viral , Genes Virais , Recombinação Genética , Fagos T/enzimologia , Replicação ViralRESUMO
The effect of temperature on genetically well-defined mutational pathways was examined in the bacteriophage T4. The mutational site was a T4 rII ochre mutant which could revert to rII+ via a transversion or to the amber convertant via a transition. Temperature did not strongly affect any of the pathways examined in a wild-type background; however, increased temperature reduced the mutational activity of a mutator DNA polymerase mutant. Possible models to explain the role of temperature in mutagenesis are discussed as well as the significance of low temperatures for in vitro mutagenesis reactions.
