Figure 7.

Transformation of DB7. (A) UV sensitivity testing of representative strains. Nutrient broth cultures of strains to be tested were streaked on a nutrient agar plate, which was UV irradiated at 254 nm for indicated time with appropriate masking and incubated. 1, ATCC4698; 2, DB7; 3, DB7 (survivor of the irradiation); 4, putative transformant. (B) UV endonuclease activity of crude extracts. Cells from late-logarithmic phase cultures in nutrient broth (5 ml) were suspended in 0.75 ml of 5 mM potassium phosphate buffer (pH 7.0) containing 10% (vol/vol) glycerol, lyzed by lysozyme treatment (at 1 mg/ml and 37°C for 15 min), and sonicated. After centrifuging the sonicates at 12,000 rpm for 10 min in the cold, 2-μl portions of the supernatants were used for the assay. Even-numbered lanes, photosensitization-treated pUC18 substrate; odd-numbered lanes, untreated substrate. Extracts used: none (lanes 1 and 2), DB7 (lanes 3 and 4), the transformant (lanes 5 and 6). cc, closed circles; oc, open circles.