POSSIBLE INVOLVEMENT OF MEMBRANE DAMAGE IN THE IN ACTIVATION BY BROAD-BAND NEAR-UV RADIATION IN Saccharomyces cerevisiae CELLS

Multiple cellular effects of near-UV radiation (300-380 nm) on inactivation, disruption of the permeability barrier and induction of gene conversion at the trp 5 locus were simultaneously measured in the same culture of a diploid strain of the yeast Saccharomyces cerevisiae in order to assess the critical lethal damage. Inactivation of exponential phase cells in water appeared to be closely related to the disruption of the permeability barrier. Inactivation and membrane damage were remarkably oxygen dependent, whereas the induction of genetic changes was very low and dependent much less on oxygen. The dependence on the temperature for inactivation and membrane damage was both low, conforming with the expectation that the processes are mainly photochemical and not enzymatic. These features are very contrasted with the characteristics of far-UV radiation effects. Possible involvement of membrane damage in near-UV inactivation of exponential phase yeast cells is discussed.