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At least 163 records · Page 9Linked to original sources
PubMed2004

Statistical analysis of the spatial distribution of operons in the transcriptional regulation network of Escherichia coli.

We have performed a statistical analysis of the spatial distribution of operons along the DNA in the transcriptional regulation network of Escherichia coli. The analysis reveals that pairs of operons that regulate each other and those that are co-regulated tend to lie much closer to one another than would be expected for a random network. Moreover, these pairs of operons tend to be transcribed in diverging directions. This spatial arrangement of operons allows the upstream regulatory domains to overlap and interfere with each other and our analysis also demonstrates the statistical significance of this motif of overlapping operons. Overlapping operons afford additional regulatory control, such as the correlated or anticorrelated expression of operons. We show by a mean-field analysis of a feed-forward loop that overlapping operons can drastically enhance the performance of gene regulatory networks. Our results suggest that regulatory control can provide a selective pressure that drives operons together in the course of evolution.

DNA, Bacterial↗
PubMed2006

The frataxin-encoding operon of Caenorhabditis elegans shows complex structure and regulation.

The genome of the nematode Caenorhabditis elegans is unusual among eukaryotes, in that it contains operons. Approximately 15% of genes in the worm are clustered into groups of between two and eight genes, which are under the control of shared regulatory sequences. Polycistronic transcripts from such operons are trans-spliced, during transcription, to produce mature monocistronic messengers. The C. elegans frataxin gene, frh-1, is encoded in the operon CEOP2232. This is one of the largest operons identified thus far in the C. elegans genome. Here we describe in detail the structure of all of the coding units within this operon. The operon is composed of eight genes of a diverse nature, organized in a complex structure. We have produced transgenic strains carrying fusions between gfp and a number of genes from the operon. These constructs show complex differential expression patterns that suggest the presence of internal promoters and regulatory sequences in the operon. This organization would permit both coordinated expression and differential expression of the components of the CEOP2232 operon. The heterogeneity of the genes, and their complex expression patterns, suggests that the clustering of CEOP2232 is not due to a need for synchronized expression of genes involved in the same physiological pathway.

Animals↗
PubMed2000

Comparative analysis of the whole set of rRNA operons between an enterohemorrhagic Escherichia coli O157:H7 Sakai strain and an Escherichia coli K-12 strain MG1655.

Two primer sets for direct sequence determination of all seven rRNA operons (rrn) of Escherichia coli have been developed; one is for specific-amplification of each rrn operon and the other is for direct sequencing of the amplified operons. Using these primer sets, we determined the nucleotide sequences of seven rrn operons, including promoter and terminator regions, of an enterohemorrhagic E. coli (EHEC) O157:H7 Sakai strain. To elucidate the intercistronic or intraspecific variation of rrn operons, their sequences were compared with those for the K-12 rrn operons. The rrn genes and the internal transcribed spacer regions showed a higher similarity to each other in each strain than between the corresponding operons of the two strains. However, the degree of intercistronic homogeneity was much higher in the EHEC strain than in K-12. In contrast, promoter and terminator regions in each operons were conserved between the corresponding operons of the two strains, which exceeded intercistronic similarity.

Base Sequence↗
PubMed2001

Sequence heterogeneity of the ten rRNA operons in Clostridium perfringens.

We have cloned and sequenced rRNA operons of Clostridium perfringens strain 13 and analyzed the sequence structure in view of the phylogenesis. The organism had ten copies of rRNA operons all of that comprised of 16S, 23S and 5S rDNAs except for one operon. The operons clustered around the origin of replication, ranging within one-third of the whole genome sequence as it is arranged in a circle. Seven operons were transcribed in clockwise direction, and the remaining three were transcribed in counter clockwise direction assuming that the gyrA was transcribed in clockwise direction. Two of the counter clockwise operons contained tRNA(Ile) genes between the 16S and 23S rDNAs, and the other had a tRNA(Ile) genes between the 16S and 23S rDNAs and a tRNA(Asn) gene in the place of the 5S rDNA. Microheterogeneity was found within the rRNA structural genes and spacer regions. The length of each 16S, 23S and 5S rDNA were almost identical among the ten operons, however, the intergenic spacer region of 16S-23S and 23S-5S were variable in the length depending on loci of the rRNA operons on the chromosome. Nucleotide sequences of the helix 19, helix 19a, helix 20 and helix 21 of 23S rDNA were divergent and the diversity appeared to be correlated with the loci of the rRNA operons on the chromosome.

Base Sequence↗
PubMed2004

Genome-wide operon prediction in Staphylococcus aureus.

Identification of operon structure is critical to understanding gene regulation and function, and pathogenesis, and for identifying targets towards the development of new antibiotics in bacteria. Recently, the complete genome sequences of a large number of important human bacterial pathogens have become available for computational analysis, including the major human Gram-positive pathogen Staphylococcus aureus. By annotating the predicted operon structure of the S.aureus genome, we hope to facilitate the exploration of the unique biology of this organism as well as the comparative genomics across a broad range of bacteria. We have integrated several operon prediction methods and developed a consensus approach to score the likelihood of each adjacent gene pair to be co-transcribed. Gene pairs were separated into distinct operons when scores were equal to or below an empirical threshold. Using this approach, we have generated a S.aureus genome map with scores annotated at the intersections of every adjacent gene pair. This approach predicted about 864 monocistronic transcripts and 533 polycistronic operons from the protein-encoding genes in the S.aureus strain Mu50 genome. When compared with a set of experimentally determined S.aureus operons from literature sources, this method successfully predicted at least 91% of gene pairs. At the transcription unit level, this approach correctly identified at least 92% of complete operons in this dataset. This consensus approach has enabled us to predict operons with high accuracy from a genome where limited experimental evidence for operon structure is available.

Chromosome Mapping↗
PubMed1999

Transcriptional regulation in response to oxygen and nitrate of the operons encoding the [NiFe] hydrogenases 1 and 2 of Escherichia coli.

Synthesis of the [NiFe] hydrogenases 1 and 2 of Escherichia coli is induced in response to anaerobiosis and is repressed when nitrate is present in the growth medium. The hydrogenase 1 and hydrogenase 2 enzymes are encoded by the polycistronic hyaABCDEF and hybOABCDEFG operons, respectively. Primer extension analysis was used to determine the initiation site of transcription of both operons. This permitted the construction of single-copy lacZ operon fusions, which were used to examine the transcriptional regulation of the two operons. Expression of both was induced by anaerobiosis and repressed by nitrate, which is in complete accord with earlier biochemical studies. Anaerobic induction of the hyb operon was only partially dependent on the FNR protein and, surprisingly, was enhanced by an arcA mutation. This latter result indicated that ArcA suppresses anaerobic hyb expression and that a further factor, which remains to be identified, is involved in controlling anaerobic induction of operon expression. Nitrate repression of hyb expression was mediated by the NarL/NarX and NarP/NarQ two-component regulatory systems. Remarkably, a narP mutant lacked anaerobic induction of hyb expression, even in the absence of added nitrate. Anaerobic induction of hya expression was dependent on the ArcA and AppY regulators, which confirms earlier observations by other authors. Nitrate repression of the hya operon was mediated by both NarL and NarP. Taken together, these data indicate that although the hya and hyb operons share common regulators, there are important differences in the control of expression of the individual operons.

Anaerobiosis↗
PubMed2004

A suf operon requirement for Fe-S cluster assembly during iron starvation in Escherichia coli.

The suf and isc operons of Escherichia coli have been implicated in Fe-S cluster assembly. However, it has been unclear why E. coli has two systems for Fe-S cluster biosynthesis. We have examined the regulatory characteristics and mutant phenotypes of both operons to discern if the two operons have redundant functions or if their cellular roles are divergent. Both operons are similarly induced by hydrogen peroxide and the iron chelator 2,2'-dipyridyl, although by different mechanisms. Regulation of the isc operon is mediated by IscR, whereas the suf operon requires OxyR and IHF for the response to oxidative stress and Fur for induction by iron starvation. Simultaneous deletion of iscS and most suf genes is synthetically lethal. However, although the suf and isc operons have overlapping functions, they act as distinct complexes because the SufS desulphurase alone cannot substitute for the IscS enzyme. In addition, suf deletion mutants are more sensitive to iron starvation than isc mutants, and the activity of the Fe-S enzyme gluconate dehydratase is diminished in the suf mutant during iron starvation. These findings are consistent with the model that the isc operon encodes the housekeeping Fe-S cluster assembly system in E. coli, whereas the suf operon is specifically adapted to synthesize Fe-S clusters when iron or sulphur metabolism is disrupted by iron starvation or oxidative stress.

Base Sequence↗
PubMed1990

The cyanase operon and cyanate metabolism.

Cyanase is an inducible enzyme in E. coli that catalyzes bicarbonate-dependent decomposition of cyanate. It is encoded as part of an operon we have named the cyn operon, which includes three genes in the following order: cynT (cyanate permease), cynS (cyanase), and cynX (protein of unknown function). The direction of transcription is opposite to that of the lac operon, and the 3'-end of the cyn operon overlaps the 3'-end of the lac operon by 98 nucleotides. The gene cynR (regulatory protein) is located upstream from the cyn operon, and its transcription is opposite that of the cyn operon. The genes of the cyn operon and the cynR gene have been cloned, sequenced and over-expressed. Cyanate at concentrations of about 1 mM is toxic to strains of E. coli lacking the cyanase gene, but strains in which the inducible gene for cyanase is present can grow on cyanate as the sole source of nitrogen at concentrations as high as 20 mM. The presence of cyanase itself is not sufficient to overcome cyanate toxicity--the permease must also be present. Strains lacking the cyanase gene, but having a functional permease gene, are extremely sensitive to cyanate. Uptake of cyanate involves the product of the permease gene in an energy-dependent process. It appears that the cyn operon has evolved to function in detoxification/decomposition of cyanate arising from both intra- and extracellular sources.

Aminohydrolases↗
PubMed1993

Structural analysis of the Actinobacillus pleuropneumoniae-RTX-toxin I (ApxI) operon.

Actinobacillus pleuropneumoniae-RTX-toxin I (ApxI), an important virulence factor, is secreted by serotypes 1, 5, 9, 10, and 11 of A. pleuropneumoniae. However, sequences homologous to the secretion genes apxIBD of the ApxI operon are present in all 12 serotypes except serotype 3. The purpose of this study was to determine and compare the structures of the ApxI operons of the 12 A. pleuropneumoniae serotypes. We focused on the nucleotide sequence comparison of the ApxI-coding genes, the structures of the ApxI operons, and the transcription of the ApxI operons. We determined the nucleotide sequences of the toxin-encoding apxICA genes of serotype 9 and found that the gene for the structural toxin, apxIA, was almost identical to the apxIA gene of serotype 1. The toxin-encoding genes of the other serotypes are also similar for the main part; nevertheless, two variants were identified, one in serotypes 1, 9, and 11 and one in serotypes 5 and 10. The two apxIA variants differ mainly within the distal 110 nucleotides. Structural analysis demonstrated that intact ApxI operons, consisting of the four contiguous genes apxICABD, are present in serotypes 1, 5, 9, 10, and 11. ApxI operons with a major deletion in the apxICA genes are present in serotypes 2, 4, 6, 7, 8, and 12. Serotype 3 does not contain ApxI operon sequences. We found that all ApxI operons are transcriptionally active despite the partial deletion of the operon in some serotypes. The implications of these data for the expression and secretion of ApxI and the other Apx-toxins, ApxII and ApxIII, as well as for the development of a subunit vaccine against A. pleuropneumoniae will be discussed.

Actinobacillus pleuropneumoniae↗
PubMed1972

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.

Binding Sites↗
PubMed1983

Replication origin region of Bacillus subtilis chromosome contains two rRNA operons.

The first replicating DNA fragment (BamHI-7) of the Bacillus subtilis chromosome contains two promoters for a rRNA operon. A map of restriction enzyme cleavage sites of the region of replication origin suggests the presence of a second rRNA operon in this region. Hybridization of rRNA genes (rDNA) with DNA fragments derived from the origin region by treatment with various enzymes clearly revealed two rRNA operons in this region, one at the B7-B3 junction and the other at the B5-B6 junction. The restriction enzyme cleavage sites surrounding the rRNA operons show that the operon at the B5-B6 junction corresponds to the rrnA operon. A novel operon at the B7-B3 junction was termed rrnO. Transformation by density-labeled fragments of the origin region showed that the first replicating marker, guaA, is located in the B3 fragment. From these results, a map was constructed for the first time to correlate the genetic markers with the physical structure of the replication origin region of the B. subtilis chromosome. The role of the rrnO operon in regulating the initiation of chromosomal replication is discussed, based on the fact that the promoter of the rrnO operon suppresses the replication of the plasmid carrying the promoter.

Bacillus subtilis↗
PubMed1983

Comparison of the overlapping frd and ampC operons of Escherichia coli with the corresponding DNA sequences in other gram-negative bacteria.

Specific DNA probes from Escherichia coli K-12 were used to analyze the sequence divergence of the frd and ampC operons in various species of gram-negative bacteria. These operons code for the fumarate reductase complex and the chromosomal beta-lactamase, respectively. We demonstrate that the two operons show the same general pattern of divergence, although the frd operon is considerably more conserved than is the ampC operon. The major exception is Salmonella typhimurium LT2, which shows a strong homology to the E. coli frd probe but none to the E. coli ampC probe. The operons from Citrobacter freundii and Shigella sonnei were cloned and characterized by physical mapping, Southern hybridization, and protein synthesis in minicells. In S. sonnei, as in E. coli K-12, the frd and ampC operons overlap (T. Grundström and B. Jaurin, Proc. Natl. Acad. Sci. U.S.A. 79:1111-1115, 1982). Only minor discrepancies between the two operons were found over the entire frd-ampC region. In C. freundii, the ampC and frd operons do not overlap, being separated by about 1,100 base pairs. Presumably the inducible property of the C. freundii chromosomal beta-lactamase is encoded by this 1,100-base-pair DNA segment.

Base Sequence↗
PubMed1991

Functional significance of overlapping transcripts of crtEF, bchCA, and puf photosynthesis gene operons in Rhodobacter capsulatus.

The Rhodobacter capsulatus crtEF, bchCA, and puf operons each encode products that function together to produce photosynthetic pigment-protein complexes. The crtEF operon encodes two enzymes of the carotenoid biosynthetic pathway, the bchCA operon encodes two enzymes of the bacteriochlorophyll biosynthetic pathway, and the puf operon contains six genes, four of which are known to code for proteins that bind pigment cofactors and position them in the intracytoplasmic membrane. These operons are adjacent on the chromosome and are transcribed in the same direction. Although each of these operons can be expressed from its own promoter, it is possible for transcription to begin at the crtEF promoter and continue through the bchCA and puf operons. We herein present the results of experiments which demonstrate that this overlapping transcriptional arrangement is important for establishment of normal levels of transcripts of the bchCA and puf operons and that read-through transcription from the bchCA operon contributes significantly to the expression of a pufB'::lac'Z gene fusion. Growth studies of crtF and bchC interposon mutants show that this read-through transcription is necessary for efficient transition from respiratory to photosynthetic growth modes.

Blotting, Northern↗
PubMed1995

Characterization of the umu-complementing operon from R391.

In addition to conferring resistances to antibiotics and heavy metals, certain R factors carry genes involved in mutagenic DNA repair. These plasmid-encoded genes are structurally and functionally related to the chromosomally encoded umuDC genes of Escherichia coli and Salmonella typhimurium. Three such plasmid operons, mucAB, impCAB, and samAB, have been characterized at the molecular level. Recently, we have identified three additional umu-complementing operons from IncJ plasmid R391 and IncL/M plasmids R446b and R471a. We report here the molecular characterization of the R391 umu-complementing operon. The nucleotide sequence of the minimal R plasmid umu-complementing (rum) region revealed an operon of two genes, rumA(R391) and rumB(R391), with an upstream regulatory signal strongly resembling LexA-binding sites. Phylogenetic analysis revealed that the RumAB(R391) proteins are approximately equally diverged in sequence from the chromosomal UmuDC proteins and the other plasmid-encoded Umu-like proteins and represent a new subfamily. Genetic characterization of the rumAB(R391) operon revealed that in recA+ and recA1730 backgrounds, the rumAB(R391) operon was phenotypically indistinguishable from mucAB. In contrast, however, the rumAB(R391) operon gave levels of mutagenesis that were intermediate between those given by mucAB and umuDC in a recA430 strain. The latter phenotype was shown to correlate with the reduced posttranslational processing of the RumA(R391) protein to its mutagenically active form, RumA'(R391). Thus, the rumAB(R391) operon appears to possess characteristics that are reminiscent of both chromosome and plasmid-encoded umu-like operons.

Amino Acid Sequence↗
PubMed1996

The cryptic general secretory pathway (gsp) operon of Escherichia coli K-12 encodes functional proteins.

Systematic sequencing of the Escherichia coli K-12 chromosome (GenBank entry U18997) has revealed the presence of an apparently complete operon of genes (the gspC-0 operon) similar to genes coding for components of the main terminal branch of the general secretory pathway (e.g., the Klebsiella oxytoca pulC-0 pullulanase secretion operon) and to related genes required for type IV pilus biogenesis. For example, the last gene in the gsp operon, gspO (formerly hopD), encodes a protein which is similar to several type IV prepilin peptidases. Expression of gspO from lacZp promotes cleavage of two known prepilin peptidase substrates in E. coli K-12: Neisseria gonorrhoeae type IV prepilin and K. oxytoca prePulG protein. gspO also complements a mutation in the corresponding gene (pulO) of the pullulanase secretion operon when it is expressed from lacZp. Another gene in the gsp operon, gspG (formerly hopG), encodes a protein similar to prePulG, a component of the pullulanase secretion pathway. Expression of gspG from lacZp leads to production of a protein which (i) is recognized by PulG-specific antiserum (and by antiserum against the Pseudomonas aeruginosa PulG homolog XcpG [formerly XcpT]), (ii) is processed in cells expressing gspO, and (iii) restores secretion in cells carrying a pulG mutation. The chromosomal copies of gspG and gspO are apparently not expressed, probably because of very weak transcription from the upstream region, as measured by using a chromosomal gspC-lacZ operon fusion. Thus, the gsp operon of E. coli K-12 includes at least two functional genes which, together with the rest of the operon, are probably not expressed under laboratory conditions.

Bacterial Outer Membrane Proteins↗
PubMed1999

Construction and initial characterization of Escherichia coli strains with few or no intact chromosomal rRNA operons.

The Escherichia coli genome carries seven rRNA (rrn) operons, each containing three rRNA genes. The presence of multiple operons has been an obstacle to many studies of rRNA because the effect of mutations in one operon is diluted by the six remaining wild-type copies. To create a tool useful for manipulating rRNA, we sequentially inactivated from one to all seven of these operons with deletions spanning the 16S and 23S rRNA genes. In the final strain, carrying no intact rRNA operon on the chromosome, rRNA molecules were expressed from a multicopy plasmid containing a single rRNA operon (prrn). Characterization of these rrn deletion strains revealed that deletion of two operons was required to observe a reduction in the growth rate and rRNA/protein ratio. When the number of deletions was extended from three to six, the decrease in the growth rate was slightly more than the decrease in the rRNA/protein ratio, suggesting that ribosome efficiency was reduced. This reduction was most pronounced in the Delta7 prrn strain, in which the growth rate, unlike the rRNA/protein ratio, was not completely restored to wild-type levels by a cloned rRNA operon. The decreases in growth rate and rRNA/protein ratio were surprisingly moderate in the rrn deletion strains; the presence of even a single operon on the chromosome was able to produce as much as 56% of wild-type levels of rRNA. We discuss possible applications of these strains in rRNA studies.

Chromosomes, Bacterial↗
PubMed2002

icaR encodes a transcriptional repressor involved in environmental regulation of ica operon expression and biofilm formation in Staphylococcus epidermidis.

Biofilm formation in Staphylococcus epidermidis is dependent upon the ica operon-encoded polysaccharide intercellular adhesin, which is subject to phase-variable and environmental regulation. The icaR gene, located adjacent to the ica operon, appears to be a member of the tetR family of transcriptional regulators. In the reference strain RP62A, reversible inactivation of the ica operon by IS256 accounts for 25 to 33% of phase variants. In this study, icaA and icaR regulation were compared in RP62A and a biofilm-forming clinical isolate, CSF41498, in which IS256 is absent. Predictably, ica operon expression was detected only in wild-type CSF41498 and RP62A but not in non-IS256-generated phase variants. In contrast, the icaR gene was not expressed in RP62A phase variants but was expressed in CSF41498 variants. An icaR::Em(r) insertion mutation in CSF41498 resulted in an at least a 5.8-fold increase in ica operon expression but did not significantly alter regulation of the icaR gene itself. Activation of ica operon transcription by ethanol in CSF41498 was icaR dependent. In contrast, a small but significant induction of ica by NaCl and glucose (NaCl-glucose) was observed in the icaR::Em(r) mutant. In addition, transcription of the icaR gene itself was not significantly affected by NaCl-glucose but was repressed by ethanol. Expression of the ica operon was induced by ethanol or NaCl-glucose in phase variants of CSF41498 (icaR+) but not in RP62A variants (icaR deficient). These data indicate that icaR encodes a repressor of ica operon transcription required for ethanol but not NaCl-glucose activation of ica operon expression and biofilm formation.

Biofilms↗
PubMed2003

Definition of a second Bacillus subtilis pur regulon comprising the pur and xpt-pbuX operons plus pbuG, nupG (yxjA), and pbuE (ydhL).

In Bacillus subtilis expression of genes or operons encoding enzymes and other proteins involved in purine synthesis is affected by purine bases and nucleosides in the growth medium. The genes belonging to the PurR regulon (purR, purA, glyA, guaC, pbuO, pbuG, and the pur, yqhZ-folD, and xpt-pbuX operons) are controlled by the PurR repressor, which inhibits transcription initiation. Other genes are regulated by a less-well-described transcription termination mechanism that responds to the presence of hypoxanthine and guanine. The pur operon and the xpt-pbuX operon, which were studied here, are regulated by both mechanisms. We isolated two mutants resistant to 2-fluoroadenine in which the pur operon and the xpt-pbuX operon are expressed at increased levels in a PurR-independent manner. The mutations were caused by deletions that disrupted a potential transcription terminator structure located immediately upstream of the ydhL gene. The 5' part of the ydhL leader region contained a 63-nucleotide (nt) sequence very similar to the 5' ends of the leaders of the pur and xpt-pbuX operons. Transcripts of these regions may form a common tandem stem-loop secondary structure. Two additional genes with potential leader regions containing the 63-nt sequence are pbuG, encoding a hypoxanthine-guanine transporter, and yxjA, which was shown to encode a purine nucleoside transporter and is renamed nupG. Transcriptional lacZ fusions and mutations in the 63-nt sequence encoding the possible secondary structures provided evidence that expression of the pur and xpt-pbuX operons and expression of the ydhL, nupG, and pbuG genes are regulated by a common mechanism. The new pur regulon is designated the XptR regulon. Except for ydhL, the operons and genes were negatively regulated by hypoxanthine and guanine. ydhL was positively regulated. The derived amino acid sequence encoded by ydhL (now called pbuE) is similar to the amino acid sequences of metabolite efflux pumps. When overexpressed, PbuE lowers the sensitivity to purine analogs. Indirect evidence indicated that PbuE decreases the size of the internal pool of hypoxanthine. This explains why the hypoxanthine- and guanine-regulated genes are expressed at elevated levels in a mutant that overexpresses pbuE.

Bacillus subtilis↗