RICH GROWTH MEDIUM ENHANCES ULTRAVIOLET RADIATION SENSITIVITY and INHIBITS CELL DIVISION IN ssb MUTANTS OF Escherichia coli K‐12

Abstract— –DNA single‐strand binding protein mutants ssb of Escherichia coli K‐12 exhibit much greater UV radiation sensitivity when plated on rich medium (RM) than when plated on minimal medium (MM). However, when comparing UV‐irradiated ssb‐113 cells (previously known as exrB and lexC113) incubated in RM vs MM, no difference was observed in DNA degradation or in the repair of incision breaks that arose during excision repair. Although UV‐irradiated ssb‐113 cells incubated in RM did resume DNA synthesis slightly sooner than those incubated in MM, and there was a small increase in the production of DNA double‐strand breaks in these cells, the most dramatic difference noted, however, was the much enhanced filamentation of irradiated cells incubated in RM vs MM. Therefore, we suggest that most of the RM‐enhanced U V radiation sensitivity in ssb‐113 cells is due to an inhibitory effect of RM on cell division rather than on DNA repair.