LOSS OF PHOTOREACTIVABILITY DURING LIQUID-HOLDING IN ESCHERICHIA COL1 WP2

Loss of photoreactivability during liquid-holding occurs much faster in Escherichia coli WP2 than has been reported for another strain of B/r (Harm, 1968). The underlying mechanism considerably reduces the maximum photoreactivation attainable within 30 min. The addition of caffeine to UV irradiated strain WP2 prevents the loss of photoreactivation activity. Similarly, a uvr A mutant also fails to show this loss of photoreactivation capacity. These results are consistent with the view that in WP2 the initial steps of excision repair take place during liquid-holding and that they can preclude photoreactivation at a high rate. But it remains to be elucidated why different strains of B/r differ with respect to this rate.