Ethidium bromide mutagenesis in Saccharomyces cerevisiae: Modulation by growth medium components

• Published in: Mutation Research/Environmental Mutagenesis and Related Subjects Vol. 46; no. 4; pp. 269 - 284
• Main Authors: Gardella, Roberta S., Macquillan, Anthony M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.1977
• Subjects: Binding Sites; Cell Division - drug effects; Culture Media; DNA; Drug Resistance, Microbial; Ethidium - pharmacology; Mitochondria - drug effects; Mitochondria - metabolism; Mutagens; Oxygen Consumption - drug effects; Saccharomyces cerevisiae - drug effects; Saccharomyces cerevisiae - metabolism
• ISSN: 0165-1161; 0027-5107
• DOI: 10.1016/0165-1161(77)90004-8

Modifications can be introduced into ethidium bromide (EB) sensitivity of yeast cells by alterations of the culture media. Our observations on several medium components which modify the mutagenic response are described, with emphasis on potassium lactate whose mode and site of action have been investigated in more detail. Interference in petite mutant induction was noted when yeast cells encountered potassium lactate prior to, during, and following EB exposure; however, more pronounced influences were observed in the first two cases. Which parameters of mutagenesis were modified was dependent on the time of contact with the substrate. Screening of other respiratory substrates for their capacity to inhibit mutagenesis uncovered an equivalent capability for potassium pyruvate and a lesser but substantial role for ethanol. The ionic composition of potassium lactate was an important determinant in its inhibitory potential, while its metabolism was found of little, if any significance. In vitro complexing of the mutagen to DNA was strongly inhibited in the presence of potassium lactate. The ionic species potassium pyruvate and KCl possessed a similar capacity to hinder EB-DNA complex formation. A correlation existed between the capability to inhibit binding in vitro and the ability to inhibit induction of the petite mutation. The association between EB and yeast mitochondria was also found to be sensitive to the presence of potassium lactate. A demonstrable and reproducible decrease in the level of drug binding to the organelles, plus a substantial degree of protection from inhibition of O 2 uptake by EB were evidence that potassium lactate influenced EB interaction with mitochondria. Because the eventual expression of EB-induced mutations can be modified by a number of cultural conditions, the use of EB mutation data suffers a limited usefulness. The extreme dependence of the mutagenic process on the composition of growth media emphasizes the need for specification of experimental conditions and calls for caution in comparison of parameters of EB induction among laboratories.