Both caffeine-induced lethality and the negative liquid holding effect, in UV- or γ-irradiated wild-type Schizosaccharomyces pombe, are consequences of interference with a recombinational repair process

✍ Scribed by Gentner, Norman E.

• Publisher: Springer
• Year: 1981
• Tongue: English
• Weight: 591 KB
• Volume: 181
• Category: Article
• ISSN: 0026-8925
• DOI: 10.1007/bf00425598

✦ Synopsis

UV-or 7-irradiated G2 phase cells of rad + Schizosaccharomycespombe show increased inactivation if incubated postirradiation, in liquid growth medium containing caffeine, before being plated on normal agar medium. The following, however, do not show such caffeine-induced lethality: G1 phase rad + cells; ascospores of a rad + strain; either G2 or G1 phase cells of the recombination-deficient radl strain; unirradiated rad + cells. Of the above, only the G2 phase rad + cells possess, at the time of radiation exposure, the capability for recombination. These results indicate that a recombinational process is responsible for caffeine-induced lethality after exposure to UV or ionizing radiation.

Similarly, the negative liquid holding effect (a progressive inactivation seen if UV-or 7-irradiated cells are incubated in non-nutritive medium such as buffer before being plated) is manifested only in G2 phase rad + cells, and not in either G1 phase rad + cells or radl cells (whether G2 or GI phase). Both the negative liquid holding effect and caffeine-induced lethality therefore are seen only in cells which fulfill all of the following conditions: (a) they must be genetically recombination-proficient; (b) they must possess at the time of irradiation the necessary two DNA copies with which to perform recombinational repair (for a haploid cell, this means they must be in G2 phase); (c) their DNA must be damaged, such as by UV or 7-ray exposure, thus requiring that recombinational repair capability be exercised in order to maintain viability; and (d) they must be incubated under conditions that fail to support the normal progress of recombinational repair. The exercising of recombinational repair capability has been shown to require an incubation medium capable of supporting growth. The incubation conditions that give rise to further inactivation of irradiated cells (non-nutritive liquid holding medium in the case of the negative liquid holding effect and exposure to caffeine in the case of caffeine-induced lethality) have been demonstrated not to support recombinational repair.