title: Missense suppression in Coprinus lagopus associated wtih a chromosome duplication.
abstract: Amongst some 70 recessive suppressors of a met-I mutation in Coprinus lagopus, one unstable suppressor was identified. The unstable suppressor, designated sup-6plus, could be maintained on minimal medium, but was lost within 24h 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-6plus yielded three types of colony: the unstable parental type, the stable met-I auxotroph and a stable prototroph which was slow-growing and inhibited by methionine in the growth medium. This stable sup-6plus type was recovered with difficulty by resolving dikaryons formed between the unstable sup-6plus strain and strains carring the wild-type allele of the suppressor gene. From sexual crosses, neither the unstable nor stable sup-6plus type segregated, only the met-I auxotrophic revertant. The unstable sup-6plus strain is thought to have an extra chromosome carrying the sup-6plus 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.
mesh_terms: D000363:Agaricales / Q000378:metabolism*; D000483:Alleles; D002467:Cell Nucleus; D002875:Chromosomes; D003302:Coprinus / Q000254:growth & development / Q000378:metabolism*; D003433:Crosses, Genetic; D004171:Diploidy; D008715:Methionine / Q000378:metabolism*; D008858:Microscopy, Phase-Contrast; D009154:Mutation; D012343:RNA, Transfer; D013172:Spores, Fungal / Q000254:growth & development; D013237:Stereoisomerism; D013489:Suppression, Genetic
chemical_list: D012343:RNA, Transfer; D008715:Methionine