ABSTRACT
Transport of cyclic AMP across Escherichia coli membrane was studied using membrane vesicles. Uptake of cyclic AMP was measured using normally oriented vesicles, whereas uptake in everted vesicles was taken as a measure of the efflux of cyclic AMP. Ultraviolet irradiation of the cells led to an inhibition of both uptake and efflux of cyclic AMP across the membrane. The presence of cyclic AMP in the growth medium prior to ultra-violet irradiation caused an enhancement of the uptake and efflux. The uptake and efflux of cyclic AMP were less in vesicles from glucose grown cells as compared to the uptake and efflux by the vesicles prepared from glycerol grown cells. Similarly both uptake and efflux of cyclic AMP were more in vesicles prepared from cells grown on glycerol or glucose in the presence of cyclic AMP than in vesicles from cells grown in absence of cyclic AMP. It is suggested that the number of cyclic AMP carrier molecules were reduced in cells under catabolite repression by glucose as well as by ultra-violet irradiation.
ABSTRACT
In Physarum polycephalum, transcription is significantly inhibited for the whole of the ultra violet-induced, extended G2 phase. Although, there is some increase in the rate of transcription closer to the first post-irradiation mitosis, thereafter, ovrall synthesis continues to be low. Also, the plasmodia developed significant resistance to actinomycin D during this period. The resistance is both in terms of mitosis and RNA synthesis. The overall depression in transcription and the drug resistance are apparently related phenomena.