Enhanced canavanine uptake is associated with nucleotide permeability in a thymidylate auxotroph of Saccharomyces cerevisiae.

The recovery of spontaneous canavanine-resistant mutants is reduced dramatically in a strain of Saccharomyces cerevisiae that carries a suppressed can 1-100 allele and is permeable to and auxotrophic for thymidylate. This effect does not occur in an isogenic strain that neither takes up nor requires the nucleotide. However, it is observed for another isogenic strain which is permeable to but not auxotrophic for thymidylate, indicating that the effect is related to thymidylate permeability. Apparently, increased sensitivity of the permeable cells to growth inhibition by canavanine accounts for the diminished mutant recovery. In turn, enhanced uptake of canavanine in these cells seems to be responsible for the increased sensitivity. The experimental findings suggest that the elevated transport of canavanine in the thymidylate auxotroph is unlikely to be due to enhanced suppression of the can 1-100 allele or to activation of the yeast general amino acid permease.