The effect of 5-bromouracil treatment on diploid yeast cells.

Abstract

The effect of treating diploid yeast cells of the constitution ade2/ + with 5-bromouracil has been studied. A synthetic medium containing aminopterin was used to create a condition of thymine starvation. 5-bromouracil or thymine were added to the blocked system to overcome the inhibition. It was expected, firstly, that incorporation of 5-BU or Th into the cells would result in growth and secondly, the effect of such an incorporation on mitotic crossing-over and/or gene conversion would result in an increase in sectored colonies. In the first series of experiments, the final concentration of Apt, 5-BU or Th was 100 μg/ml. In the second series two different concentrations of 5-BU were tested, viz. 50 μg/ml and 100 μg/ml. The treated suspensions were aerated for 40 hours at 28°C. The results demonstrate Apt-caused inhibition of DNA synthesis as anticipated. No significant increase in growth was observed between suspensions with Apt alone and with Apt and 5-BU or Th added. This indicates that neither 5-BU nor Th were incorporated into the cells of Saccharomyces cerevisiae when Apt was present. It was also observed that Apt-treated cells plated on agar medium formed significantly higher frequencies of sectored colonies than cells from control suspensions.