Construction of hybrid plasmids containing the lysA gene of Escherichia coli: studies of expression in Escherichia coli and Saccharomyces cerevisiae

Native SILAC: metabolic labeling of proteins in prototroph microorganisms based on lysine synthesis regulation

Mass spectrometry (MS)-based quantitative proteomics has matured into a methodology able to detect and quantitate essentially all proteins of model microorganisms, allowing for unprecedented depth in systematic protein analyses. The most accurate quantitation approaches currently require lysine auxotrophic strains, which precludes analysis of most existing mutants, strain collections, or commercially important strains (e.g. those used for brewing or for the biotechnological production of metabolites). Here, we used MS-based proteomics to determine the global response of prototrophic yeast and bacteria to exogenous lysine. Unexpectedly, down-regulation of lysine synthesis in the presence of exogenous lysine is achieved via different mechanisms in different yeast strains. In each case, however, lysine in the medium down-regulates its biosynthesis, allowing for metabolic proteome labeling with heavy-isotope-containing lysine. This strategy of native stable isotope labeling by amino acids in cell culture (nSILAC) overcomes the limitations of previous approaches and can be used for the efficient production of protein standards for absolute SILAC quantitation in model microorganisms. As proof of principle, we have used nSILAC to globally analyze yeast proteome changes during salt stress.

Dynamic change in promoter activation during lysine biosynthesis in Escherichia coli cells

We investigated the expression dynamics of genes involved in lysine biosynthesis in Escherichia coli cells to obtain a quantitative understanding of the gene regulatory system. By constructing reporter strains expressing the green fluorescence protein (gfp) gene under the control of the promoter regions of those genes associated with lysine biosynthesis, time-dependent changes in gene expression in response to changes in lysine concentration in the medium were monitored by flow cytometry. Five promoters involved in lysine biosynthesis respond to the changes in lysine concentration in the medium. For these five promoters, time-dependent gene expression data were fitted to a simple dynamical model of gene expression to estimate the parameters of the gene regulatory system. According to the fitting parameters, dapD shows a significantly larger coefficient of repression than the other genes in the lysine synthesis pathway, which indicates the weak binding activity of the repressor to the dapD promoter region. Moreover, there is a trend that the closer an enzyme is to the start of the lysine biosynthesis pathway, the smaller its maximal promoter activity is. The results provide a better quantitative understanding of the expression dynamics in the lysine biosynthesis pathway.

Identification of chromosomal Shigella flexneri genes induced by the eukaryotic intracellular environment

Upon entry into the eukaryotic cytosol, the facultative intracellular bacterium Shigella flexneri is exposed to an environment that may necessitate the expression of particular genes for it to survive and grow intracellularly. To identify genes that are induced in response to the intracellular environment, we screened a library containing fragments of the S. flexneri chromosome fused to a promoterless green fluorescent protein gene (gfp). Bacteria containing promoter fusions that had a higher level of gfp expression when S. flexneri was intracellular (in Henle cells) than when S. flexneri was extracellular (in Luria-Bertani broth) were isolated by using fluorescence-activated cell sorting. Nine different genes with increased expression in Henle cells were identified. Several genes (uhpT, bioA, and lysA) were involved in metabolic processes. The uhpT gene, which encoded a sugar phosphate transporter, was the most frequently isolated gene and was induced by glucose-6-phosphate in vitro. Two of the intracellularly induced genes (pstS and phoA) encode proteins involved in phosphate acquisition and were induced by phosphate limitation in vitro. Additionally, three iron-regulated genes (sufA, sitA, and fhuA) were identified. The sufA promoter was derepressed in iron-limiting media and was also induced by oxidative stress. To determine whether intracellularly induced genes are required for survival or growth in the intracellular environment, we constructed mutations in the S. flexneri uhpT and pstS genes by allelic exchange. The uhpT mutant could not use glucose-6-phosphate as a sole carbon source in vitro but exhibited normal plaque formation on Henle cell monolayers. The pstS mutant had no apparent growth defect in low-phosphate media in vitro but formed smaller plaques on Henle cell monolayers than the parent strain. Both mutants were as effective as the parent strain in inducing apoptosis in a macrophage cell line.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

Heterologous expression and regulation of the lysA genes of Pseudomonas aeruginosa and Escherichia coli

The Pseudomonas aeruginosa lysA gene encoding diaminopimelate decarboxylase (DAP-decarboxylase) was cloned into a broad host range vector. This gene complemented a lys mutation at the lys-12 locus of P. aeruginosa and a lysA defect in Escherichia coli. The P. aeruginosa DAP-decarboxylase was synthesized constitutively in P. aeruginosa as well as in E. coli, where the Pseudomonas lysA gene was poorly expressed. By contrast, the E. coli lysA gene was expressed well in P. aeruginosa and subject to lysine regulation when the E. coli LysR activator protein was provided. This indicates that the mechanism of transcriptional activation for the E. coli lysA gene is effective in the heterologous host.

Cloning and expression in Escherichia coli of genes involved in the lysine pathway of Brevibacterium lactofermentum

The Brevibacterium lactofermentum genes which complement Escherichia coli lysA and asd-1 mutants were identified, respectively, as a 1.9-kilobase PstI-ClaI fragment and a 2.5-kilobase PstI fragment by cloning into pBR325. Southern blot transfers show hybridization to chromosomal fragments of identical size. The putative B. lactofermentum asd and lysA products are 44 and 48 kilodaltons, respectively.

Regulatory pattern of the Escherichia coli lysA gene: expression of chromosomal lysA-lacZ fusions

The regulation of lysA which encodes the last enzyme for lysine biosynthesis in Escherichia coli, diaminopimelic acid-decarboxylase, was studied by using lysA-lacZ fusions. Our results indicate an absolute requirement for the LysR product for its activation, LysR protein present in a limiting amount which can be titrated by a multicopy plasmid carrying its target site and a negative regulatory role for the LysA protein itself which decreases lysA-lacZ expression 30-fold.

Nucleotide sequence of the promoter region of the E. coli lysC gene

The regulatory region of the lysC gene (that encodes the lysine-sensitive aspartokinase of Escherichia coli) has been identified and purified by the use of lysC-lacZ fusions. Its regulatory sequence has been determined. No signals similar to those described in the case of an attenuation mechanism could be found in the long leader sequence existing between the starts of transcription and of translation.

Regulation of diaminopimelate decarboxylase synthesis in Escherichia coli. III. Nucleotide sequence and regulation of the lysR gene

The complete nucleotide sequence of the lysR gene, which encodes the activatory protein required for lysA expression, has been determined. Bal31 deletions and translational fusions were used to localize the promoter region and the initiator ATG of the lysR gene which encodes a 311 amino acid polypeptide. Both lysA and lysR coding sequences were found to be divergent and separated by a very short intergenic region consisting of 121 base-pairs between the postulated ATGs of the two proteins. Transfer of the whole lysR gene on a plasmid carrying a lysR-lacZ fusion shows that lysR expression is autoregulated by a factor of 7. The same binding site (73 base-pairs fragment) could be involved in both effects of the LysR product, acting simultaneously as an operator for lysR expression and an initiator for lysA expression. The genetic organization of the whole region (4127 base-pairs) is given. A strikingly symmetrical pattern is observed with the four tightly packed galR, lysA, lysR and orfX (an unidentified open reading frame) genes, in a very unusual arrangement of both divergent and convergent overlapping transcription units.

Regulation of diaminopimelate decarboxylase synthesis in Escherichia coli. I. Identification of a lysR gene encoding an activator of the lysA gene

The synthesis of diaminopimelate decarboxylase, which catalyzes the decarboxylation of diaminopimelate into lysine, is known to be repressed by lysine and induced by diaminopimelate in Escherichia coli K12. Until now only mutations in lysA, the structural gene for diaminopimelate decarboxylase, have been described that lead to a Lys- phenotype. A set of plasmids carrying adjacent inserts of the lysA region was constructed and employed to transform different Lys- mutants. The complementation pattern observed and the corresponding expression of the lysA gene show that in fact the Lys- phenotype can be obtained by mutations in two different and closely linked loci: one being the lysA structural gene, and the other called lysR. We propose that the lysR gene encodes a positive effector required for the full expression of the lysA gene. The synthesis of a hybrid lysA-lacZ protein constructed in vitro was observed to be decreased dramatically in lysR mutants. Moreover, all the regulatory features were lost, indicating that the LysR activator is necessary for the regulation of lysA expression. The gene order is thyA lysA lysR clockwise around 61 minutes on the chromosome, lysA being transcribed counter-clockwise.