Genetic events associated with an insertion mutation in yeast

Area of Science:

• Genetics
• Molecular Biology
• Yeast Genetics

Background:

• The his4-912 mutation in Saccharomyces cerevisiae is a null mutation affecting all three functions of the HIS4 gene.
• This mutation exhibits genetic properties resembling those induced by procaryotic insertion elements, suggesting a potential role for such elements or similar mechanisms.

Purpose of the Study:

• To investigate the genetic mechanisms underlying the reversion of the his4-912 mutation to a His+ phenotype.
• To characterize the different classes of revertants and associated chromosomal aberrations.

Main Methods:

• Isolation and characterization of His+ revertants from the his4-912 mutant strain.
• Genetic analysis to identify the nature of the mutations and chromosomal rearrangements in revertants.
• Mapping of the his4 gene region and associated aberrations.

Main Results:

• Multiple classes of His+ revertants were identified, indicating diverse reversion pathways.
• The most frequent revertants arose from site-specific mutations causing a cold-sensitive His- phenotype.
• Other revertants involved significant chromosomal rearrangements, including translocations, a transposition of the his4 region, and an inversion.
• Deletions extending from the his4-912 locus into the HIS4 gene were also observed.
• In many revertants, the his4 region was found to be closely associated with the observed chromosomal aberrations.
• Some revertants exhibited additional, unrelated chromosomal changes like duplications, deletions, and aneuploidy.

Conclusions:

• The his4-912 mutation is unstable and can be reverted through a variety of genetic events, highlighting the plasticity of the yeast genome.
• Chromosomal aberrations, including translocations, inversions, and deletions, play a significant role in the reversion of this mutation.
• The close linkage between the his4 region and chromosomal aberrations suggests that these rearrangements are directly involved in restoring HIS4 function.
• The study provides insights into mutation mechanisms and genome stability in yeast.