The radioresistant component of haploid yeast cells (SC-7) was established by previous investigators to be due to budding cells, and cells with small buds are known to be undergoing DNA synthesis. The response of budding cells of haploid strain SC-7 (Saccharomyces cerevisiae) as a function of LET was studied in this investigation by use of heavy ions (in the <tex-math>${\rm LET}_{\infty}$</tex-math> range 420 to 17000 MeV <tex-math>${\rm g}^{-1}{\rm cm}^{2}$</tex-math>) from the Berkeley heavy-ion linear accelerator. The maximum sensitivity for budding cells occurs at approximately the same <tex-math>${\rm LET}_{\infty}$</tex-math> (1300-1500 MeV <tex-math>${\rm g}^{-1}{\rm cm}^{2}$</tex-math>) as that for nonbudding cells. The radiosensitivity as a function of LET, of budding haploid yeasts relative to nonbudding cells, is found to be remarkably similar to that of S-phase Chinese hamster cells in culture relative to cells not undergoing DNA synthesis.

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