Myxin inhibits the biosynthesis of DNA in Chlamydomonas reinhardi cells. This antibiotic, however, preferentially degrades chloroplast DNA in these cells. In contrast to the stimulation of DNA degradation by myxin in the absence of protein synthesis in E. coli cells, inhibition of chloroplast and cytoplasmic protein synthesis had no effect on the DNA breakdown in Chlamydomonas. Exposure of the cells to myxin for a short duration “triggers” a DNA-degradative system which continues to function in the absence of the drug. The manifestation of the latter effect is prevented if the cells are transferred from phototrophic or mixotrophic to the heterotrophic growth following the removal of the antibiotic.
