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The Action of Phleomycin on Meiotic Cells¹

Department of Biology, University of California, San Diego, La Jolla, California 92037

The action of low concentrations of phleomycin (0.5–5 µg/ml) on the behavior of meiotic cells has been studied. At these low concentrations, the drug has no obvious effect on DNA, RNA, and protein synthesis, but it completely inhibits the entry of cells from the G₂ phase into either meiosis or mitosis. The inhibitory effect of the drug is not restricted to the G₂ phase but is equally effective at each of the subsequent stages of meiosis. The drug appears to prevent any cell development which involves changes in chromosome structure. In addition, the drug has been shown to have a cumulative effect on the structure of chromosomes. This effect manifests itself as a gradual and increasing condensation of chromosome material. Unlike the inhibitory effects which are equally pronounced at all stages, the apparent condensation of chromosomes occurs more readily at some stages than others. A brief exposure of cells to the drug is sufficient to induce the characteristic and irreversible changes.

¹ This investigation was supported by NSF Grant GB 5173X and supplemented by USPHS Grant HD03015 from the National Institute of Child Health and Human Development.

Received 12/ 9/68. Accepted 5/ 9/69.