This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hua, S.-S. Articles by Markovitz, A. Search for Related Content PubMed PubMed Citation Articles by Hua, S.-S. Articles by Markovitz, A.

Multiple Regulator Gene Control of the Galactose Operon in Escherichia coli K-12

Department of Microbiology, The University of Chicago, Chicago, Illinois 60637

ABSTRACT

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.

This article has been cited by other articles:

• Rotanova, T. V., Botos, I., Melnikov, E. E., Rasulova, F., Gustchina, A., Maurizi, M. R., Wlodawer, A. (2006). Slicing a protease: Structural features of the ATP-dependent Lon proteases gleaned from investigations of isolated domains.. Protein Sci. 15: 1815-1828 [Abstract] [Full Text]  
• Levy, S., Marshall, B, Rowse-Eagle, D, Onderdonk, A (1980). Survival of Escherichia coli host-vector systems in the mammalian intestine. Science 209: 391-394 [Abstract]