Canavanine Resistance and the Mechanism of Arginine Uptake in the Fission Yeast Schizosaccharomyces pombe

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Abstract
The mechanism of resistance to the arginine analog L-canavanine, and of arginine uptake, were examined in the fission yeast S. pombe. Two mutants with increased resistant to canavanine were analyzed genetically: both were double mutants, and in each case one mutation conferred resistance to conavanine, while the other enhanced this resistance. Evidence is presented that can1.1 strains are defective in one system for aginine uptake, which presumably presents entry of canavanine into the cell. This system operates in the wild-type whether the N source supplied is ammonium or glutamate. Double mutants carrying can1.1 and an arginine requirement are unable to grow on ammonium medium even when supplied with exogenous arginine, while growth can occur on glutamate plus arginine. This suggested the existence of a 2nd uptake system for arginine which is absent during growth on ammonium, and direct measurement of the rates of arginine uptake under various conditions confirmed this. These observations closely parallel those made on the budding yeast Saccharomyces cerevisae. The ability to select for or against function of the can1 gene should facilitate certain types of genetical analysis in S. pombe.