INCREASED PRODUCTION OF COLICIN E1 IN STATIONARY-PHASE

The synthesis of colicin E1 is known to be regulated by the SOS respon se, anaerobiosis, and catabolite repression, The expression of cea-lac Z fusions was also found to be stimulated when cells reached stationar y phase, This increase in expression was determined to be due to deple tion of nutrients from the medium, since the addition of fresh medium reversed the effect, Expression of the fusion increased when cells wer e starved in 10 mM MgSO4 and when they were grown in conditioned mediu m in which cells had been grown previously. The stimulation of express ion occurred when the cea-lacZ fusion was present in single-copy as we ll as in multicopy plasmids. Finally, the data were consistent with th is increase being independent of the SOS response, anaerobiosis, catab olite repression, and integration host factor as well as the stationar y-phase regulators encoded by rpoS and lrp.