Gene Control of Copper-Sensitivity in Saccharomyces

Abstract

AN extensive study of the adaptation of yeasts to copper by Prof. Joji Ashida and his associates¹ revealed that yeasts are trained to high concentrations of copper by a two-step process. On agar containing copper, they found that copper-sensitive yeast cells grew as a thin film which became spotted with brown colonies of copper-resistant cells. Cells which they selected from the brown colonies proliferated rapidly on transfer to a copper medium, producing dense brown subcultures. Studies by the Ashida group indicated that many factors affect pigmentation of the copper-resistant cells. They inferred that the ability to resist copper-poisoning could be transferred to sensitive cells by ribonucleic acid extracted from closely related resistant organisms, but not by ribonucleic acid from sensitive organisms. They showed that the difference between resistant and sensitive cells was clearly expressed in medium containing 1 mM/l. of copper sulphate. In the cultures of Saccharomyces tested by Ashida and his group copper-resistant variants did not arise without training; none grew rapidly on a copper medium without previous selection by the two-step process described above.