Mutagenic action of hydrostatic pressure on yeast: a cell cycle analysis.

Pressure-treated log growth cultures (14,000 psi equivalent to 966 x 10(5) N/m2 for 4 h) of Saccharomyces cerevisiae were fractionated across a linear Ficoll gradient by zonal rotor centrifugation. This procedure separated the yeast cells on the basis of size and volume into a continuum of cell cycle ages. Cell survival and petite mutation frequency were determined for several zonal fractions. Survival of yeast cells after pressure treatment was maximal in zonal fractions obtained from either the top (single cells in G1) or the botton ("doublets") of the gradient. Intermediate zonal fractions showed more lethality, with minimal survival occurring in zonal fractions containing a large proportion of yeast cells in which buds were just beginning to emerge (initiation of S phase). The petite mutation frequency was minimal in zonal fractions from the top (single cells in G1) and bottom ("doublets") of the gradient. Induction increased to a maximum in those fractions containing cells in S phase.