Yim J J, Yoon J, Park Y S, Grell E H, Jacobson K B
Biochem Genet. 1987 Jun;25(5-6):359-74. doi: 10.1007/BF00554545.
The suppressor gene, su(s)2, in Drosophila melanogaster restores the production of red and brown eye pigments for some purple and vermilion mutant alleles, respectively. We showed previously that the product of the su(s)+ allele caused inhibition of the sepiapterin synthase A produced by the purple mutant but did not affect the wild-type enzyme. Suppression was accomplished by removing su(s)+ from the genome. We now report that the tryptophan oxygenase, produced by suppressible vermilion alleles, is also inhibited by extracts from su(s)+ flies. The inhibition of the vermilion enzyme can be reduced or eliminated, respectively, by prior storage of the extract at 4 or -20 degrees C or by boiling, whereas the wild-type enzyme is not affected by extracts of su(s)+ flies. Also, when the suppressible vermilion strain is raised on certain diets, brown eye pigment production occurs. This epigenetic suppression was reduced by the presence of an extra copy of su(s)+ in the genome. These data support a posttranslational mechanism for regulation of enzyme activity in which the activity of the mutant enzyme is reduced by the product of the su(s)+ allele. How the su(s)+ gene product can distinguish between the normal and the mutant forms of these two enzymes is discussed, along with other mechanisms for suppression that are currently under investigation.
果蝇中的抑制基因su(s)2，分别能使一些紫色和朱红色突变等位基因恢复产生红色和棕色眼色素。我们之前表明，su(s)+等位基因的产物会抑制紫色突变体产生的蝶啶合酶A，但不影响野生型酶。通过从基因组中去除su(s)+实现抑制作用。我们现在报告，可被抑制的朱红色等位基因产生的色氨酸加氧酶，也会被su(s)+果蝇的提取物抑制。分别通过将提取物预先在4℃或 -20℃保存或煮沸，可降低或消除对朱红色酶的抑制作用，而野生型酶不受su(s)+果蝇提取物的影响。此外，当可被抑制的朱红色品系在特定饮食条件下饲养时，会产生棕色眼色素。基因组中额外存在一份su(s)+会降低这种表观遗传抑制作用。这些数据支持一种翻译后调节酶活性的机制，即su(s)+等位基因的产物会降低突变酶的活性。文中讨论了su(s)+基因产物如何区分这两种酶的正常形式和突变形式，以及目前正在研究的其他抑制机制。
