Dark and light repair in ultraviolet-irradiated Acholeplasma laidlawii

Abstract

The ultraviolet sensitivity and repair capability of Acholeplasma laidlawii were investigated. Ultraviolet sensitivity and degree of photoreversal vary with the cells' growth phase and pass through a maximum for middle to late logarithmic phase cells. The cells also show a liquid holding recovery after irradiation. Chloramphenicol, added either before or after the ultraviolet dose, reduces the recovery by a factor of 10. Nalidixic acid has a similar effect if added before the ultraviolet, but, if added after the ultraviolet dose, the reduction in recovery is much less. Hence, liquid holding recovery may involve a DNA repair enzyme. Alkaline sucrose analysis of the cells' DNA during recovery shows the appearance of breaks and their repair. The DNA profiles also show a small molecular weight component, which may be the virus which has been isolated from these cells (A. LISS and J.Maniloff , Science, 173 (1971) 725).