Further inducibility of a constitutive system: ultrainduction of the gal operon

Tokeson, J. P. E.; Garges, Susan

doi:10.1128/jb.173.7.2319-2327.1991

Cited by 21 publications

(18 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The expression of the gal operon in the P2 promoter (in a P1 mutant) was measured in the wild type and hupA and/or hupB deleted bacterial strains. The gal expression was measured by assaying the amounts of -galactosidase synthesis in these strains in which the lacZ gene, encoding -galactosidase was fused to galT in frame (Tokeson et al 1991). The results clearly confirmed the role of HU in repression of the P2 promoter in gal.…”

Section: Derepression Of Gal Operon In Vivo In Hup Mutantssupporting

confidence: 58%

**Histone‐like protein HU as a specific transcriptional regulator: co‐factor role in repression of gal transcription by GAL repressor**

1996

View full text Add to dashboard Cite

Background: Transcription initiation from the two overlapping promoters of the gal operon in Escherichia coli is negatively regulated by binding of Gal repressor (GalR) to bipartite operators, which encompass the promoters. Coordinated repression of the two promoters requires GalR binding to both operators. In a purified system, GalR, nevertheless, fails to show the coordinated repression, predicting the participation of an additional factor(s) in the regulation in vivo.

show abstract

Section: Derepression Of Gal Operon In Vivo In Hup Mutantssupporting

confidence: 58%

**Histone‐like protein HU as a specific transcriptional regulator: co‐factor role in repression of gal transcription by GAL repressor**

1996

View full text Add to dashboard Cite

show abstract

“…5, closer to the promoter than it is in galS (+92.5). Since GalS apparently binds gal or gal-like operator sequences (27,32), we believe that isorepressor (GalS) represses galS transcription by binding to O( or 01 or both.…”

Section: Resultsmentioning

confidence: 99%

Control of transcription of gal repressor and isorepressor genes in Escherichia coli

Weickert

1993

J Bacteriol

Self Cite

View full text Add to dashboard Cite

Two regulatory proteins, Gal repressor and isorepressor, control the expression of the gal and mgl operons in Escherichia coli. The transcription start sites for gaiR and galS, the genes for the repressor and isorepressor, were determined by primer extension of in vivo transcripts. Study of the promoter-lacZ gene fusions introduced into the chromosome indicated that galS expression was elevated in cells in which the normal galS gene was interrupted, but not in cells in which the gaiR gene was deleted. When In Escherichia coli, the genes responsible for D-galactose metabolism (the galactose operon [galETK]) and for highaffinity transport of methylgalactosides, glucose, and galactose (the mglBAC operon) are controlled by a repressor, GalR (5,17,18,24), and an isorepressor, GalS (9, 32). Both operons are induced by D-galactose or by its nonmetabolizable analog, D-fucose (3,4,7,12,14,16,23,32). For GalR, inducer binding results in a loss of repressor affinity for DNA (17,18). The same mechanism is presumed to mediate mgl induction, which is under the control of GalS (32).GalR and GalS have overlapping regulatory specificities, as indicated by ultrainduction of the gal operon. In the absence of GalR, the gal operon is induced two-to fourfold by the addition of D-galactose or D-fucose (27). Ultrainduction, which occurs at the level of transcription, is mediated by GalS (9, 32), which can be titrated specifically by multiple copies of the same operators to which Gal repressor binds (27).GalS and GalR belong to the GalR-LacI family of regulators (33). Two of the other members of this family, PurR and CytR, are negatively autoregulated. Negative autoregulation of PurR is mediated by interaction of PurR with two operators downstream of the start of transcription (20,22). Repression is two-to threefold and requires hypoxanthine or guanine as a corepressor. CytR is also negatively autoregulated by twofold when CytR is supplied on a low-copynumber plasmid to cells containing a fusion of the cytR promoter and the lacZ gene (8). The cytR promoter contains one cytR operator upstream of the transcription start site. We investigated whether the Gal repressor and isorepressor are regulated, autoregulated, or cross-regulated. We present evidence that galS is (i) negatively autoregulated and (ii) positively regulated by cyclic AMP (cAMP) receptor protein (CRP) and that galR is constitutively expressed. MATERIALS AND METHODSBacterial strains, plasmids, phage, and growth conditions. A list of bacterial strains and plasmids used in this study is presented in Table 1. Bacteriophage Plvir was from our laboratory collection, and XNT5 (6) was a gift from N. Trun. The transfer of AgalR::Cmr, galS::TnlO (Tcr), or Acrp::Cmr to strain MC4100 or its derivatives was by bacteriophage P1-mediated transduction followed by selection for resistance of the transductants to the appropriate antibiotics. Phage XNT5 contains a promoterless, truncated lacZ gene and a truncated bla gene incapable of conferring resistance to ampicillin (Apr). Lysates of X...

show abstract

“…(The strains used in this study are shown in Table 1.) In such a strain, ultrainduction was indicated by a threefold increase in ,-galactosidase activity when the inducer was added (10). Colonies of such a strain appeared red on MacConkey lactose plates, even in the absence of an inducer, because of the high level of expression (approximately 500 Miller units; see Table 2).…”

mentioning

confidence: 99%

A mutation defining ultrainduction of the Escherichia coli gal operon

et al. 1991

Self Cite

View full text Add to dashboard Cite

Tn1O insertion in the galS (ultrainduction factor) gene of Escherichia coli allows the gal operon to be constitutively expressed at a very high level, equal to that seen in a AgalR strain in the presence of an inducer. The insertion has been mapped by criss-cross Hfr matings and by marker rescue into Kohara phages at 46 min on the E. coli chromosome.The gal operon of Escherichia coli is regulated both positively and negatively at the level of transcription initiation. There are two gal promoters, P1 and P2; P1 is activated by the cyclic AMP-cyclic AMP receptor protein complex bound in the -40 region, whereas P2 is inhibited by this binding. To isolate a mutation in the gene encoding the second repressor, we started with a strain that was deleted for the galR gene and had a galE-lacZ protein fusion (JT247). (The strains used in this study are shown in Table 1.) In such a strain, ultrainduction was indicated by a threefold increase in ,-galactosidase activity when the inducer was added (10). Colonies of such a strain appeared red on MacConkey lactose plates, even in the absence of an inducer, because of the high level of expression (approximately 500 Miller units; see Table 2). When the P-galactosidase competitive inhibitor thio-ethyl-phenyl-,-D-galactoside (TEPG) (5) of these MC4100 Tcr colonies were pooled, and phage P1 was grown on the bacterial pool. The resulting P1 lysate was used to infect JT247, selecting for tetracycline resistance on Luria broth plates containing 15 ,ug of tetracycline per ml. Tetracycline-resistant colonies were replicaplated to MacConkey lactose plates containing 15 ,ug of tetracycline per ml and 1 mM TEPG. Red colonies were found at a frequency of approximately 1.0%.To ensure that the red phenotype on MacConkey lactosetetracycline-TEPG plates was caused by the ATnJO insertion, phage P1 was used to transfer the ATnJO from six of the mutants into a fresh JT247 strain. In one of the six, there was no linkage (O of 226 tetracycline-resistant colonies) between tetracycline resistance and the MacConkey lactose plate phenotype. In each of the other five, 100% of at least 2,000 tetracycline-resistant colonies were red on the MacConkey lactose-tetracycline-TEPG plates. Only these five were studied further.,-Galactosidase in the mutants was measured and compared with that in the parent strain. Results are shown in Table 2. Two classes of mutants were found: class I, four mutants that in the absence of an inducer had a high level of gal-lacZ expression which increased further upon addition of an inducer (represented by strain AG708); and class II, one mutant that in absence of an inducer had a high level of expression of gal-lacZ which did not increase upon addition of an inducer (strain AG701). The phenotype of the second class was what we expected from a mutation in a gene encoding the proposed second gal repressor. Expression was at a high level regardless of whether an inducer was present. We call the gene into which the ATnJO was inserted galS. The mutation in AG708 is probably not allelic...

show abstract

Further inducibility of a constitutive system: ultrainduction of the gal operon

Cited by 21 publications

References 27 publications

**Histone‐like protein HU as a specific transcriptional regulator: co‐factor role in repression of gal transcription by GAL repressor**

**Histone‐like protein HU as a specific transcriptional regulator: co‐factor role in repression of gal transcription by GAL repressor**

Control of transcription of gal repressor and isorepressor genes in Escherichia coli

A mutation defining ultrainduction of the Escherichia coli gal operon

Contact Info

Product

Resources

About