Full text loading...
Missense Suppression in Coprinus lagopus Associated with a Chromosome Duplication
Abstract
SUMMARY: Amongst some 70 recessive suppressors of a met-1 mutation in Coprinus lagopus, one unstable suppressor was identified. The unstable suppressor, designated sup-6 +, could be maintained on minimal medium, but was lost within 24 h on minimal medium containing more than 1.7 p.p.m. dl-methionine or 0·75 p.p.m. l-methionine. Isolation of hyphal tips from the monokaryotic strain carrying sup-6 + yielded three types of colony: the unstable parental type, the stable met-1 auxo-troph and a stable prototroph which was slow-growing and inhibited by methionine in the growth medium. This stable sup-6 + type was recovered with difficulty by resolving dikaryons formed between the unstable sup-6 + strain and strains carrying the wild-type allele of the suppressor gene. From sexual crosses, neither the unstable nor stable sup-6 + type segregated, only the met-1 auxotrophic revertant. The unstable sup-6 + strain is thought to have an extra chromosome carrying the sup-6 + mutation. For vigorous growth the wild-type allele, sup-6 -, is indispensable and would be carried on the homologous chromosome. The selective pressures on different media account for loss of the duplicated chromosomes. The results are interpreted as missense suppression by a mutant of an indispensable tRNA.
- Received:
- Revised:
- Published Online:
© Society for General Microbiology, 1975