Lewis D, Casselton L A
J Gen Microbiol. 1975 May;88(1):20-6. doi: 10.1099/00221287-88-1-20.
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.
在鬼伞属的约70个met-I突变隐性抑制子中，鉴定出一个不稳定的抑制子。这个不稳定的抑制子被命名为sup-6plus，它能在基本培养基上维持，但在含有超过1-7 ppm DL-甲硫氨酸或0-75 ppm L-甲硫氨酸的基本培养基上24小时内就会丢失。从携带sup-6plus的单核菌株中分离菌丝尖端，产生了三种类型的菌落：不稳定的亲本类型、稳定的met-I营养缺陷型和一种稳定的原养型，后者生长缓慢且在生长培养基中受甲硫氨酸抑制。通过解析不稳定的sup-6plus菌株与携带抑制基因野生型等位基因的菌株之间形成的双核体，很难恢复这种稳定的sup-6plus类型。在有性杂交中，不稳定的和稳定的sup-6plus类型都不发生分离，只有met-I营养缺陷型回复体。不稳定的sup-6plus菌株被认为有一条额外的染色体携带sup-6plus突变。为了实现旺盛生长，野生型等位基因sup-6是必不可少的，它将位于同源染色体上。不同培养基上的选择压力导致了重复染色体的丢失。这些结果被解释为一个不可或缺的tRNA突变体的错义抑制。
