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Regulation of lactose utilization genes in Staphylococcus xylosus.

ABSTRACT: The lactose utilization genes of Staphylococcus xylosus have been isolated and characterized. The system is comprised of two structural genes, lacP and lacH, encoding the lactose permease and the beta-galactosidase proteins, respectively, and a regulatory gene, lacR, coding for an activator of the AraC/XylS family. The lactose utilization genes are divergently arranged, the lacPH genes being opposite to lacR. The lacPH genes are cotranscribed from one promoter in front of lacP, whereas lacR is transcribed from two promoters of different strengths. Lactose transport as well as beta-galactosidase activity are inducible by the addition of lactose to the growth medium. Primer extension experiments demonstrated that regulation is achieved at the level of lacPH transcription initiation. Inducibility and efficient lacPH transcription are dependent on a functional lacR gene. Inactivation of lacR resulted in low and constitutive lacPH expression. Expression of lacR itself is practically constitutive, since transcription initiated at the major lacR promoter does not respond to the availability of lactose. Only the minor lacR promoter is lactose inducible. Apart from lactose-specific, LacR-dependent control, the lacPH promoter is also subject to carbon catabolite repression mediated by the catabolite control protein CcpA. When glucose is present in the growth medium, lacPH transcription initiation is reduced. Upon ccpA inactivation, repression at the lacPH promoter is relieved. Despite this loss of transcriptional regulation in the ccpA mutant strain, beta-galactosidase activity is still reduced by glucose, suggesting another level of control.

SUBMITTER: Bassias J

PROVIDER: S-EPMC107164 | biostudies-literature | 1998 May

REPOSITORIES: biostudies-literature

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Regulation of lactose utilization genes in Staphylococcus xylosus.

Bassias J J Brückner R R

Journal of bacteriology 19980501 9

The lactose utilization genes of Staphylococcus xylosus have been isolated and characterized. The system is comprised of two structural genes, lacP and lacH, encoding the lactose permease and the beta-galactosidase proteins, respectively, and a regulatory gene, lacR, coding for an activator of the AraC/XylS family. The lactose utilization genes are divergently arranged, the lacPH genes being opposite to lacR. The lacPH genes are cotranscribed from one promoter in front of lacP, whereas lacR is t ...[more]

PMID: 9573174

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Project description:In Staphylococcus xylosus, scrB is one of two genes necessary for sucrose utilization. It encodes a sucrase that hydrolyzes intracellular sucrose-6-phosphate generated by the uptake of sucrose via the sucrose-specific enzyme II of the phosphotransferase system, the gene product of scrA. ScrB sucrase activity is inducible by the presence of sucrose in the culture medium. Primer extension experiments demonstrated that the observed regulation is achieved at the level of scrB transcription initiation. The protein mediating sucrose-specific regulation of scrB was found to be encoded immediately upstream of the sucrase gene. The nucleotide sequence of the regulatory gene scrR comprises an open reading frame that specifies a protein of 35.8 kDa. This protein exhibits similarity to transcriptional regulators of the GalR-LacI family. Inactivation of the scrR reading frame in the genome of S. xylosus led to the constitutive expression of scrB at a high level, identifying ScrR as a repressor of transcription. Sucrose-specific regulation of scrB was also lost upon deletion of 4 bp of a palindromic sequence (OB) covering positions +6 to +21 downstream of the scrB transcriptional start site. These results suggested a direct interaction of the ScrR repressor and the operator OB. Accordingly, a fusion protein consisting of the maltose-binding protein of Escherichia coli and the ScrR protein was able to interact with an scrB promoter fragment in gel mobility shift experiments but failed to bind an scrB fragment carrying the 4-bp deletion derivative of OB. An scrR promoter fragment, which dose not contain a sequence resembling OB, was not shifted by the fusion protein. This result corroborates scrR primer extension analyses showing that transcription of the repressor gene itself is not regulated. Therefore, the sucrase gene operator OB is the target sequence through which the ScrR protein exerts its negative effect on transcription initiation. In the promoter region of scrA, the gene essential for sucrose transport, two palindromic sequences that are similar to the scrB operator are found. Their presence in scrA suggests that ScrR controls a sucrose-specific regulon in S. xylosus.

Dataset Information

Regulation of lactose utilization genes in Staphylococcus xylosus.

Publications

Regulation of lactose utilization genes in Staphylococcus xylosus.

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