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SUMMARY: Chlamydomonas reinhardi, starved of arginine, stopped growing but remained viable and continued to make protein. Synthesis of DNA and the accumulation of stable species of RNA were severely inhibited. Synthesis of rapidly labelled RNA was initially inhibited, but only temporarily, and finally rapidly labelled RNA was made faster than with arginine. These disturbances in nucleic acid metabolism were not related to changes in the pool sizes of nucleotide triphosphates, nor were any new nucleotides, such as guanosine tetraphosphate, detectable. When arginine in the medium was replaced by canavanine, the cells lost their chlorophyll, became non-motile, and non-viable. Canavanine rapidly inhibited the synthesis of RNA, but only inhibited the incorporation of amino acids into protein or the synthesis of DNA after a long lag. The size of the pools of nucleotide triphosphates and the pattern of their labelling with adenine was changed. These effects were consistent with a mechanism of killing, involving replacement of arginine by canavanine, by the cytoplasmic protein-synthesizing system. This protein then prevented all RNA synthesis. No changes in the structure of the nucleus were detected. Chlamydomonas reinhardi, therefore, differs from Escherichia coli in its response to arginine starvation or treatment with canavanine.

The Effects of Canavanine and of Arginine Starvation on Macromolecular Synthesis in Chlamydomonas reinhardi