Stimulation ofDerepressed EnzymeSynthesis inBacteria by Growth onSublethal Concentrations ofChloramphenicol

respectively, wasenhanced three- to10-fold ascompared tocultures notexposed to CAP.Enhancement of,B-galactosidase synthesis byprior exposure toCAPwas also observed inuracil-starved E.coli cultures. Stimulation ofenzymesynthesis appeared tobeaspecific effect ofCAP;lowlevels oferythromycin, puromycin, sparsomycin, tetracycline, andrifampin didnotshowsucheffects. Derepression ofATCasesynthesis inexponentially growing cells inthepresence ofCAPdidnot result instimulation ofenzymesynthesis byCAP.Aprior history ofgrowth ofa culture inthepresence ofCAPwasshowntobenecessary forenhancement of enzymesynthesis byCAP;furthermore, continued presence ofCAP inthe mediumduring starvation wasnotnecessary forenhanced enzymesynthesis and inhibited itinsomeinstances. Enhanced enzymesynthesis instarving, CAPtreated cultures couldbeblocked byrifampin, whichsuggested thatCAP treatment allows prolonged ormoreextensive messenger ribonucleic acid synthesis. Ithasbeenknownforsometimethat growth ofbacteria inthepresence oflowconcentrations oftheantibiotic chloramphenicol (CAP)causes effects on enzymesynthesis thatcannotbe explained assimply resulting fromgeneral inhibition ofprotein synthesis. Sypherd etal.(30, 32)andPaigen (25) haveshownthat thesynthesisof,3-galactosidase andother inducible enzymeswasinhibited toafargreater extent than total protein synthesis whenEscherichia coli cells wereinduced while growing inthepresence oflowconcentrations (0.5 to1.0,g/ml) ofCAP. Synthesis ofseveral "constitutive" enzymes was notpreferentially inhibited. Lowconcentrations ofother antibiotic inhibitors ofprotein synthesis, butnotother growth inhibitors, also preferentially inhibited synthesis of,8-galactosidase. Further studies bySypherd andDeMoss(29) eliminated thepossibility thattheeffects of CAPwereamanifestation ofcatabolite repressionashadbeensuggested byothers (21, 25). Preferential inhibition off,-galactosidase or tryptophan synthetase synthesis byCAP was showntorequire functional regulatory genes (i+ ortrpR+, respectively) (29). Furthermore, preferential inhibition off,-galactosidase synthesis couldbeshowntoresult froma variety of