ACTION SPECTRUM FOR GROWTH DELAY INDUCED BY NEAR-ULTRAVIOLET LIGHT IN E. coli B/r K*

Abstract— The action spectrum for growth delay induced by near-uv light was determined for Escherichia coli B/r growing in a defined medium. This spectrum agrees with and extends that determined earlier by Jagger and his co-workers for E. coli B growing in nutrient broth. The extended spectrum is indistinguishable from the absorption spectrum for 4-thiouridine above 320 nm, but deviates significantly at wavelengths shorter than this from the spectrum for 8–13 link formation in transfer RNA containing 4-thiouridine at position 8. These results extend the evidence that 4-thiouridine in transfer RNA is the chromophore for near-UV induction of growth delay, but weaken the case for linkage of a pyrimidine at position 13 in transfer RNA as the mechanism of growth delay.