Figure 6. swi7-1 mutation causes genetic instability.

A. Quantification of Rad22-YFP foci in swi7-1 mutant and wild-type cells. Wild type (ENY670) and swi7 (MK140) mutant cells expressing Rad22-YFP were grown at room temperature until the mid-log phase. A small aliquot of cell culture was used for analysis by microscopy. About six hundred cells were analysed for each strain. B. Line drawing displaying the different cell morphologies through the cell cycle in fission yeast. C. Assay for quantification of recombination frequencies. Schematic drawing of the intrachromosomal recombination substrate and of the possible outcomes of recombination events. The red circles indicate the approximate positions of the mutations. D. Quantification of the recombination rate in wild-type (JZ518) and swi7 (MK226) mutant strains. The histograms displays the recombination rates for the substrate shown in panel E. Rates of total number, conversion- and deletion-type recombination events are shown. The given values are the means of recombination frequencies for independent colonies. E. Visualization of recombination rates by growth on media containing limited adenine. swi7 mutant displays increased sectoring on YE medium due to recombination at the direct repeats of ade6 in the substrate. Cells with ade6⁻ mutations in the intact substrate turn red on YE medium due to accumulation of a slightly toxic red pigment. Cells with the recombined wild type ade6⁺ gene do not accumulate the pigment and are white (sectors in swi7 colony).