Spontaneous mutation at the mtr locus of Neurospora: the spectrum of mutant types
Abstract:
We have isolated 135 strains of Neurospora which have mutations at the mtr locus resulting from independent spontaneous events. mtr is the structural gene for the neutral amino acid permease. The mutants have been characterized by their reversion behavior (both spontaneous and induced) and by hybridization studies of restriction digests of their DNA. About half of the mutants (54%) appear to result from single base-pair substitutions. Thirty-four percent have deletions, including some which extend into neighboring genes. Most of the remaining mutants have insertions. Several of the insertions are tandem duplications of 400-1000 bp and these mutants are unstable, reverting to mtr+ with a high frequency. When tandem-duplication mutants go through a cross, they are modified: the mutant progeny are fully stable. This modification is probably due to RIP (repeat-induced point mutation). This process has an important bearing on the comparison of germinal to somatic mutation.
Insights
Researchers studied 135 Neurospora strains with mutations in the mtr gene, identifying the causes of these mutations. They found that repeat-induced point mutation (RIP) can stabilize unstable mutations during genetic crosses.
Area of Science:
- Genetics
- Molecular Biology
- Biochemistry
Background:
- The mtr locus in Neurospora encodes the neutral amino acid permease, crucial for amino acid transport.
- Understanding mutation mechanisms is fundamental to genetics and molecular biology.
Purpose of the Study:
- To characterize spontaneous mutations at the mtr locus in Neurospora.
- To investigate the molecular basis and behavior of these mtr mutations.
Main Methods:
- Isolation and characterization of 135 independent mtr mutant strains.
- Analysis of spontaneous and induced reversion frequencies.
- DNA hybridization studies using restriction digests.
Main Results:
- 54% of mutants resulted from single base-pair substitutions.
- 34% involved deletions, some affecting adjacent genes.
- Remaining mutants had insertions, including unstable tandem duplications (400-1000 bp).
- Tandem-duplication mutants became stable after genetic crosses, likely due to repeat-induced point mutation (RIP).
Conclusions:
- Spontaneous mutations at the mtr locus are diverse, including substitutions, deletions, and insertions.
- Repeat-induced point mutation (RIP) is a significant factor in stabilizing unstable mutations during genetic crosses in Neurospora.
- RIP influences the comparison between germinal and somatic mutation rates.
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