Regulation of Lac Transcription in Escherichia coli by Cyclic Adenosine 3',5'-Monophosphate

Transcription and regulation of the cpdB gene in Escherichia coli K12 and Salmonella typhimurium LT2: evidence for modulation of constitutive promoters by cyclic AMP-CRP complex

Measurements of cyclic phosphodiesterase, or of beta-galactosidase in the case of cpdB'-'lacZ fusions, indicate that cpdB expression in both Escherichia coli and Salmonella typhimurium is modulated by carbon source availability, consistent with previous observations in Salmonella. Nucleotide sequence analysis and transcription mapping of both cpdB genes have revealed, in their 5' flanking regions, sequences with good similarity to consensus -10 and -35 regions and cyclic AMP-cyclic AMP receptor protein (cAMP-CRP) binding sites. Furthermore, they are strongly conserved in both organisms. Deletion analysis of an E. coli cpdB'-'lacZ fusion supports the identification of these elements, and a role for the cAMP-CRP binding site in modulating constitutive cyclic phosphodiesterase expression.

Dual promoter control of the Escherichia coli lactose operon

The control of transcription initiation at the lactose operon promoter was investigated in vitro. We found that an upstream promoter (termed lac P2) interfered with RNA polymerase binding at the principal promoter (termed lac P1). The start site for lac P2 was located at base pair position -22 relative to the P1 start site. The addition of cAMP receptor protein and cAMP was shown to repress lac P2 and to activate lac P1. Abortive initiation reactions for both promoters were used to investigate the coordinate repression-activation elicited by CRP-cAMP. The effects of lac promoter mutations (L8, Ps, and UV5) were consistent with an important RNA polymerase positioning role for CRP-cAMP in the activation of lac operon expression.

Effects of phagocytosis by rabbit granulocytes on macromolecular synthesis and degradation in different species of bacteria

Phagocytosis and killing of gram-positive Bacillus megaterium and Micrococcus lysodeikticus by granulocytes in vitro is associated with almost immediate cessation of bacterial protein synthesis. By contrast, protein synthesis by Escherichia coli continues after ingestion and killing. After preincubation of E. coli with intact granulocytes for 15 min, when 95% or more of the bacteria can no longer multiply, induction of beta-galactosidase proceeds at rates about half of control values. With disrupted granulocytes, which kill E. coli as rapidly as intact cells, the rate of induction of beta-galactosidase does not fall until after 30 min of preincubation. We attribute the different effects of phagocytosis on the biochemical apparatus of these microorganisms to the different fates of their envelopes. Specifically labeled protein, ribonucleic acid, deoxyribonucleic acid, and lipid of all three species of bacteria and peptidoglycan of E. coli are apparently incompletely degraded during phagocytosis. However, the cell walls of M. lysodeikticus and B. megaterium undergo rapid and almost complete degradation. The resulting structural disintegration of these gram-positive microorganisms must cause extensive biochemical disorganization as well. Our evidence indicates that the E. coli envelope, on the other hand, retains sufficient structural organization to preserve integrated biochemical function for at least 1 h after the bacteria have lost the ability to multiply.

Multiple regulator gene control of the galactose operon in Escherichia coli K-12

Previous studies showed that nonsense mutations in either of two genes (capR or capS) or an undefined mutation in a third gene (capT) led to pleiotropic effects: (i) increased capsular polysaccharide synthesis (mucoid phenotype); (ii) increased synthesis of enzymes specified by at least four spatially separated operons involved in synthesis of capsular polysaccharide including the product of the galE gene, UDP-galactose-4-epimerase (EC 5.1.3.2) in capR mutants. The present study demonstrated that the entire galactose (gal) operon (galE, galT, and galK) is derepressed by mutations in either the capR or the capT genes, but not by mutation in capS. Double mutants (capR9 capT) were no more derepressed than the capR9 mutant, indicating that capR9 and capT regulate the gal operon via a common pathway. Isogenic double mutants containing either galR(+), galR(-), galR(s), or galO(c) in combination with either capR(+) or capR9 were prepared and analyzed for enzymes of the gal operon. The results demonstrated that capR9 caused derepression as compared to capR(+) in all of the combinations. Strains with a galR(s) mutation are not induced, for the gal operon, by any galactose compound including d-fucose, and this was confirmed in the present study using d-fucose. Nevertheless, the derepression of galR(s) capR9 compared to galR(s) capR(+) was four- to sixfold. The same derepression was observed when galR(+)capR9 was compared to galR(+)capR(+). The data eliminate the explanation that internal induction of the gal operon by a galactose derivative was causing increased gal operon enzyme synthesis in capR or capT mutants. Furthermore, the same data suggest that the galR and capR genes are acting independently to derepress the gal operon. A modified model for the structure of the gal operon is proposed to explain these results. The new feature of the model is that two operator sites are suggested, one to combine with the galR repressor and one to combine with the capR repressor.