Figure 1.

Isolation of the mutant strain sr22 in the screening. (A) Enrichment of high-density cells by Percoll density gradient centrifugation four times after UV irradiation (+) or not (−). The cells cultured for six days on S medium were separated by Percoll density gradient centrifugation (90%). The bottoms (3 mL) of the sample fractions after the centrifugation were subjected to sorting or single colony isolation. (B) Differential interference contrast (DIC) microscopy images of UV-untreated cells in the total fraction and UV-treated cells in the total and high-density fractions.