The initial steps in assimilation of sulfate during cysteine biosynthesis entail sulfate uptake and sulfate activation by formation of adenosine 5'-phosphosulfate, conversion to 3'-phosphoadenosine 5'-phosphosulfate, and reduction to sulfite. Mutations in a previously uncharacterized Escherichia coli gene, cysQ, which resulted in a requirement for sulfite or cysteine, were obtained by in vivo insertion of transposons TnStacl and TnSsupF and by in vitro insertion of resistance gene cassettes. cysQ is at chromosomal position 95.7 min (kb 4517 to 4518) and is transcribed divergently from the adjacent cpdB gene. A TnStacl insertion just inside the 3' end of cysQ, with its isopropyl-4-D-thiogalactopyranoside-inducible tac promoter pointed toward the cysQ promoter, resulted in auxotrophy only when isopropyl-4-D-thiogalactopyranoside was present; this conditional phenotype was ascribed to collision between converging RNA polymerases or interaction between complementary antisense and cysQ mRNAs. The auxotrophy caused by cysQ null mutations was leaky in some but not all E. coli strains and could be compensated by mutations in unlinked genes. cysQ mutants were prototrophic during anaerobic growth. Mutations in cysQ did not affect the rate of sulfate uptake or the activities of ATP sulfurylase and its protein activator, which together catalyze adenosine 5'-phosphosulfate synthesis. Some mutations that compensated for cysQ null alleles resulted in sulfate transport defects. cysQ is identical to a gene called amtA, which had been thought to be needed for ammonium transport. Computer analyses, detailed elsewhere, revealed significant amino acid sequence homology between cysQ and suhB of E. coli and the gene for mammalian inositol monophosphatase. Previous work had suggested that 3'-phosphoadenoside 5'-phosphosulfate is toxic if allowed to accumulate, and we propose that CysQ helps control the pool of 3'-phosphoadenoside 5'-phosphosulfate, or its use in sulfite synthesis.The cysteine biosynthetic pathway (Fig. 1), a principal route of sulfur assimilation, involves more than 15 genes in at least five chromosomal regions in Escherichia coli and Salmonella typhimurium. It has been studied since the early days of physiological genetics in order to elucidate the roles of the individual genes, the control of their expression, and how the flow of metabolic intermediates is regulated (for a review, see reference 25). The transcription of most cys genes is positively controlled by the protein product of cysB and its coinducer, O-acetyl serine (also a cysteine precursor), during aerobic growth; transcription is repressed by sulfide, which is generated by reversal of the final biosynthetic step (Fig. 1). CysB seems not to be needed during anaerobic growth (3). The cysQ gene described here is also needed only during aerobic growth. It is inferred to act before sulfite formation, and hence this early part of the cysteine pathway is reviewed briefly below.The initial step, sulfate uptake, is mediated by a permease encoded by the cysT, cysW,...
In carbohydrate-based fermentations of Saccharopolyspora erythraea, a polar knockout of the methylmalonyl-CoA mutase (MCM) gene, mutB, improved erythromycin production an average of 126% (within the range of 102-153% for a 0.95 confidence interval). In oil-based fermentations, where erythromycin production by the wild-type strain averages 184% higher (141-236%, 0.95 CI) than in carbohydrate-based fermentations, the same polar knockout in mutB surprisingly reduced erythromycin production by 66% (53-76%, 0.95 CI). A metabolic model is proposed where in carbohydrate-based fermentations MCM acts as a drain on the methylmalonyl-CoA metabolite pool, and in oil-based fermentations, MCM acts in the reverse direction to fill the methylmalonyl-CoA pool. Therefore, the model explains, in part, how the well-known oil-based process improvement for erythromycin production operates at the biochemical level; furthermore, it illustrates how the mutB erythromycin strain improvement mutation operates at the genetic level in carbohydrate-based fermentations.
Engineering of the methylmalonyl-CoA (mmCoA) metabolite node of the Saccharopolyspora erythraea wild type strain (FL2267) through duplication of the mmCoA mutase (MCM) operon led to a 51% (range 40%-64%, 0.95 CI, N = 152) increase in erythromycin production in a highperformance oil-based fermentation medium. The MCM operon was carried on a 6.8 kb DNA fragment in plasmid pFL2212 which was inserted by homologous recombination into the S. erythraea chromosome. The fragment contained one uncharacterized gene, ORF1; three MCM related genes, mutA, mutB, meaB; and one gntR-family regulatory gene, mutR. Additional strains were constructed containing partial duplications of the MCM operon, as well as a knockout of ORF1, none of these strains showed any significant alteration in their erythromycin production profile. The combined results showed that increased erythromycin production only occurred in strain FL2385 containing a duplication of the entire MCM operon including mutR and a predicted stem-loop structure overlapping the 3′ terminus of the mutR coding sequence.
BackgroundEarly screening for prostate cancer (PCA) remains controversial because of overdiagnosis and overtreatment of clinically insignificant cancers. Even though a number of diagnostic tests have been developed to improve on PSA testing, there remains a need for a more informative non-invasive test for PCA. The objective of this study is to identify a panel of DNA methylation markers suitable for a non-invasive diagnostic test from urine DNA collected following a digital rectal exam (DRE) and/or from first morning void (FV). A secondary objective is to determine if the cumulative methylation is indicative of biopsy findings.MethodsDRE and FV urine samples were prospectively collected from 94 patients and analyzed using 24 methylation-specific quantitative PCR assays derived from 19 CpG islands. The methylation of individual markers and various combinations of markers was compared to biopsy results. A methylation threshold for cancer classification was determined using a target specificity of 70%. The average methylation and the number of positive markers were also compared to the result of the biopsy, and the area under the receiver operating characteristic curves (AUCs) were calculated.ResultsMethylation of all 19 markers was detected in FV and DRE DNAs. Combining the methylation of two or more markers improved on individual marker results. Using 6of19 methylated markers as the threshold for cancer classification yielded a specificity of 71% (95% CI, 0.57–0.86) from both DRE and FV and a sensitivity of 89% (95% CI, 0.79–0.97) from DRE and 94% (95% CI, 0.84–1.0) from FV. The negative predictive value at the 6of19 threshold was ≥ 90 for both DNA types.ConclusionsPCA-specific methylation was detected in both FV and DRE DNA. There was no significant difference in diagnostic accuracy at the 6of19 threshold between DRE and FV urine DNA. The results support the development of a non-invasive diagnostic test to reduce unnecessary biopsies in men with elevated PSA. The test can also provide patients with personalized recommendations based on their own methylation profile.Electronic supplementary materialThe online version of this article (10.1186/s13148-018-0524-x) contains supplementary material, which is available to authorized users.
Derivatives of Escherichia coli K-12 of known ancestry were characterized by random amplified polymorphic DNA (RAPD) fingerprinting to better understand genome evolution in this family of closely related strains. This sensitive method entails PCR amplification with arbitrary primers at low stringency and yields arrays of anonymous DNA fragments that are strain specific. Among 150 fragments scored, eight were polymorphic in that they were produced from some but not all strains. Seven polymorphic bands were chromosomal, and one was from the F-factor plasmid. Five of the six mapped polymorphic chromosomal bands came from just 7% of the genome, a 340-kb segment that includes the terminus of replication. Two of these were from the cryptic Rac prophage, and the inability to amplify them from some strains was attributable to deletion (excision) or to rearrangement of Rac. Two other terminus-region segments that resulted in polymorphic bands appeared to have sustained point mutations that affected the ability to amplify them. Control experiments showed that RAPD bands from the 340-kb terminus-region segment and also from two plasmids (P1 and F) were represented in approximate proportion to their size. Optimization experiments showed that the concentration of thermostable polymerase strongly affected the arrays of RAPD products obtained. Comparison of RAPD polymorphisms and positions of strains exhibiting them in the pedigree suggests that many sequence changes occurred in these historic E. coli strains during their storage. We propose that the clustering of such mutations near the terminus reflects errors during completion of chromosome replication, possibly during slow growth in the stab cultures that were often used to store E. coli strains in the early years of bacterial genetics.Nearly half a century has passed since Gray and Tatum reported the first isolation of laboratory-generated nutritional mutations in Escherichia coli K-12 (7). Thousands of derivatives of the original strain have been generated since then, and the ancestries of many of them are known from Bachmann's painstaking tracing of pedigrees in publications and scattered laboratory notes (2, 3). Some early derivatives arose spontaneously, but most were induced, often with heavy doses of radiation or chemical mutagens. Diverse mutant phenotypes were selected; among the most frequent were requirements for particular amino acids or other metabolites, the inability to utilize particular carbon sources, and resistances to phages and other antimicrobial agents.We have studied DNA sequence level divergence among historic E. coli K-12 strains, using the arbitrary primer PCR (or RAPD, for random amplified polymorphic DNA) method of DNA fingerprinting (27, 30) to better understand how these strains have evolved. In this method, single oligonucleotides of arbitrarily chosen sequence are used as primers in low-stringency PCRs. Arrays of DNA fragments are generated that reflect annealing of the primer to closely linked pairs of sites that fortuitously match or part...
Background Prostate cancer diagnosis using the PSA test remains controversial because of overdiagnosis and overtreatment of potentially indolent cancers. There remains a need to increase the diagnostic lead time and to target treatment to patients with significant disease. One possible approach to overcome the limitations of PSA is to screen men for the molecular signature of early PCA, monitor the rate of disease progression and target treatment to patients who are likely to benefit from it. Such an approach requires a large panel of markers that define a molecular clock for PCA. We recently developed a panel of 19 markers for the non-invasive detection of PCA from urine DNA. It raised the possibility that additional methylation markers could be successfully analyzed from urine DNA, a prerequisite for increasing the diagnostic lead time and enabling disease monitoring. Methods We developed semi-quantitative polymerase chain reaction assays for 13 additional markers and determined their methylation status in 150 urine DNAs from 94 patients with elevated PSA. Eighty five samples were obtained following DRE and 65 samples were from first void. We combined the data of the 13 new markers with the previously reported 19 markers and calculated the sensitivity, specificity, negative and positive predictive values at every threshold from one to 32 positive markers. Results Using 10of32 positive markers as the threshold to recommend a biopsy yields a sensitivity of 81% (95% CI 0.68–0.93) and 93% (95% CI 0.84–1.02) and a specificity of 76% (95% CI 0.63–0.88) and 77% (95% CI 0.63–0.91) from DRE and FV DNA, respectively. The PPV was 71% and 77% and the NPV was 85% and 93% from DRE and FV, respectively. Conclusions This study shows that large marker panels can be analyzed from urine DNA without loss of sensitivity or specificity. Using 32 markers improved the stratification of patients undergoing screening for PCA particularly for patients below the 10of32 threshold. The results show the utility of larger biomarker panels for PCA diagnosis and suggest that the development of the panels needed to monitor disease progression could be successfully accomplished. Electronic supplementary material The online version of this article (10.1186/s40164-019-0137-x) contains supplementary material, which is available to authorized users.
Multiprotein complexes regulate the transcription of certain bacterial genes in a sensitive, physiologically responsive manner. In particular, the transcription of genes needed for utilization of nucleosides in Escherichia coli is regulated by a repressor protein, CytR, in concert with the cyclic AMP (cAMP)-activated form of cAMP receptor protein (CRP). We studied this regulation by selecting and characterizing spontaneous constitutive mutations in the promoter of the udp (uridine phosphorylase) gene, one of the genes most strongly regulated by CytR. We found deletions, duplications, and point mutations that affect key regulatory sites in the udp promoter, insertion sequence element insertions that activated cryptic internal promoters or provided new promoters, and large duplications that may have increased expression by udp gene amplification. Unusual duplications and deletions that resulted in constitutive udp expression that depended on the presence of CytR were also found. Our results support the model in which repression normally involves the binding of CytR to cAMP-CRP to form a complex which binds to specific sites in the udp promoter, without direct interaction between CytR protein and a specific operator DNA sequence, and in which induction by specific inducer cytidine involves dissociation of CytR from cAMP-CRP and then RNA polymerase interaction with cAMP-CRP bound to a site upstream of the transcription start point. The stimulation of udp expression by CytR in certain mutants may reflect its stabilization of cAMP-CRP binding to target DNA and illustrates that only modest evolutionary changes could allow particular multiprotein complexes to serve as either repressors or transcriptional activators.Multiprotein complexes, long recognized as regulators of expression of many eukaryotic genes, can also be important in the regulation of prokaryotic gene expression (1). This is exemplified by the genes encoding the array of membrane proteins and intracellular enzymes that take up and catabolize deoxy-and ribonucleosides in Escherichia coli (19). Much of the expression of nucleoside utilization genes is coordinated by a repressor protein, CytR, acting in concert with the cyclic AMP (cAMP)-activated form of the cAMP receptor protein (CRP) (2, 9, 27). The three promoters that have been analyzed most extensively (deoP2, cddP, and tsxP) each contain two binding sites for CRP (CRP1 and CRP2) but are otherwise dissimilar in sequence (Fig. 1). The current view is that transcription from these promoters involves CRP binding to CRP1 and that repression involves the binding of CytR protein to CRPs that are, in turn, bound to both CRP1 and CRP2 in the promoter region. It had been speculated that CytR binding to specific DNA sequences would also be important in repression, since CytR exhibits considerable homology to other repressors (21, 32). An imperfect inverted-repeat motif (5Ј-TGCAAN 2-3 TTGCA) is present in each of these promoters and is considered a candidate CytR recognition sequence (24). In this model, inductio...
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