Effect of potassium nitrate on photoreactivation of Escherichia coli cells.

Photoreactivation is the repair of ultraviolet radiation damage in a biological system with light of wavelength longer than that of the damaging radiation (Jagger1). A wide variety of ultraviolet induced effects may be reversed by photoreactiva­ tion, including killing, mutations, division delay, block in the DNA synthesis, etc. Such photoreactiva­ tion effects generally involve the photoenzymatic splitting of cyclobutane-type pyrimidine dimers in the DNA (R upert2) . The effect of potassium nitrate was examined on the photorekctivation of colony forming ability of ultraviolet irradiated Escherichia coli cells and on in v ivo monomerization of ultraviolet induced thy­ mine dimers in the bacterial cell’s own DNA during photoreactivation.