Effect of pyrimethamine on the morphology and ultrastructure of Saccharomyces cerevisiae.

Sub-lethal levels of the folate analogue, pyrimethamine, caused pronounced cell elongation in Saccharomyces cerevisiae strain B41 when grown in glycerol medium. The orientation of bud development was also altered. Electron microscopy of thin sections showed an increase in cell wall thickness, but apart from this and the overall cell shape, the ultrastructure of the cells was normal. The structural abnormalities are attributed to alterations in the plasmalemma caused by protein synthesis inhibition in the mitochondria.