Missense suppression in Coprinus lagopus associated wtih a chromosome duplication

Area of Science:

• Genetics
• Molecular Biology
• Mycology

Background:

• Recessive suppressors are crucial for understanding gene regulation and function.
• Methionine biosynthesis pathways are essential for fungal growth.
• Unstable genetic elements can provide insights into chromosome dynamics and mutation mechanisms.

Purpose of the Study:

• To characterize an unstable recessive suppressor mutation (sup-6plus) in Coprinus lagopus.
• To investigate the genetic basis and stability of the sup-6plus mutation.
• To elucidate the mechanism of suppression and its relationship with methionine metabolism.

Main Methods:

• Isolation and characterization of recessive suppressors of a met-I mutation.
• Maintenance and manipulation of fungal strains on different growth media.
• Genetic analysis including isolation of hyphal tips, formation of dikaryons, and sexual crosses.
• Analysis of chromosome segregation and stability.

Main Results:

• One unstable suppressor, sup-6plus, was identified among 70 recessive suppressors.
• sup-6plus was lost on media with DL-methionine or L-methionine.
• Isolation of hyphal tips yielded unstable, stable auxotrophic, and stable slow-growing prototrophic colonies.
• Sexual crosses showed segregation only of the met-I auxotrophic revertant, not sup-6plus types.
• The unstable sup-6plus strain is hypothesized to carry an extra chromosome.

Conclusions:

• The unstable sup-6plus mutation is likely due to a duplicated chromosome carrying the suppressor.
• Selective pressures of different media lead to the loss of duplicated chromosomes.
• The results suggest missense suppression by a mutant of an indispensable transfer RNA (tRNA).