scholarly journals Amino Acid Transport and Metabolism in Mycobacteria: Cloning, Interruption, and Characterization of anl-Arginine/γ-Aminobutyric Acid Permease inMycobacterium bovis BCG

2000 ◽  
Vol 182 (4) ◽  
pp. 919-927 ◽  
Author(s):  
Anjali Seth ◽  
Nancy D. Connell

ABSTRACT Genes encoding l-arginine biosynthetic and transport proteins have been shown in a number of pathogenic organisms to be important for metabolism within the host. In this study we describe the cloning of a gene (Rv0522) encoding an amino acid transporter fromMycobacterium bovis BCG and the effects of its deletion onl-arginine transport and metabolism. The Rv0522 gene of BCG was cloned from a cosmid library by using primers homologous to therocE gene of Bacillus subtilis, a putative arginine transporter. A deletion mutant strain was constructed by homologous recombination with the Rv0522 gene interrupted by a selectable marker. The mutant strain was complemented with the wild-type gene in single copy. Transport analysis of these strains was conducted using 14C-labeled substrates. Greatly reduced uptake of l-arginine and γ-aminobutyric acid (GABA) but not of lysine, ornithine, proline, or alanine was observed in the mutant strain compared to the wild type, grown in Middlebrook 7H9 medium. However, when the strains were starved for 24 h or incubated in a minimal salts medium containing 20 mM arginine (in which even the parent strain does not grow),l-[14C]arginine uptake by the mutant but not the wild-type strain increased strongly. Exogenousl-arginine but not GABA, lysine, ornithine, or alanine was shown to be toxic at concentrations of 20 mM and above to wild-type cells growing in optimal carbon and nitrogen sources such as glycerol and ammonium. l-Arginine supplied in the form of dipeptides showed no toxicity at concentrations as high as 30 mM. Finally, the permease mutant strain showed no defect in survival in unactivated cultured murine macrophages compared with wild-type BCG.

2004 ◽  
Vol 70 (10) ◽  
pp. 5882-5890 ◽  
Author(s):  
Shin-ichi Akazawa ◽  
Tetsuya Karino ◽  
Nobuyuki Yoshida ◽  
Tohoru Katsuragi ◽  
Yoshiki Tani

ABSTRACT Three active fractions of fructosyl-amino acid oxidase (FAOD-Ao1, -Ao2a, and -Ao2b) were isolated from Aspergillus oryzae strain RIB40. N-terminal and internal amino acid sequences of FAOD-Ao2a corresponded to those of FAOD-Ao2b, suggesting that these two isozymes were derived from the same protein. FAOD-Ao1 and -Ao2 were different in substrate specificity and subunit assembly; FAOD-Ao2 was active toward N ε-fructosyl N α-Z-lysine and fructosyl valine (Fru-Val), whereas FAOD-Ao1 was not active toward Fru-Val. The genes encoding the FAOD isozymes (i.e., FAOAo1 and FAOAo2) were cloned by PCR with an FAOD-specific primer set. The deduced amino acid sequences revealed that FAOD-Ao1 was 50% identical to FAOD-Ao2, and each isozyme had a peroxisome-targeting signal-1, indicating their localization in peroxisomes. The genes was expressed in Escherichia coli and rFaoAo2 showed the same characteristics as FAOD-Ao2, whereas rFaoAo1 was not active. FAOAo2 disruptant was obtained by using ptrA as a selective marker. Wild-type strain grew on the medium containing Fru-Val as the sole carbon and nitrogen sources, but strain ΔfaoAo2 did not grow. Addition of glucose or (NH4)2SO4 to the Fru-Val medium did not affect the assimilation of Fru-Val by wild-type, indicating glucose and ammonium repressions did not occur in the expression of the FAOAo2 gene. Furthermore, conidia of the wild-type strain did not germinate on the medium containing Fru-Val and NaNO2 as the sole carbon and nitrogen sources, respectively, suggesting that Fru-Val may also repress gene expression of nitrite reductase. These results indicated that FAOD is needed for utilization of fructosyl-amino acids as nitrogen sources in A. oryzae.


1988 ◽  
Vol 8 (8) ◽  
pp. 3150-3159
Author(s):  
R Parker ◽  
T Simmons ◽  
E O Shuster ◽  
P G Siliciano ◽  
C Guthrie

Saccharomyces cerevisiae contains at least 24 distinct small nuclear RNAs (snRNAs), several of which are known to be essential for viability and to participate in the splicing of pre-mRNAs; the RNAs in this subset contain binding sites for the Sm antigen, a hallmark of metazoan snRNAs involved in mRNA processing. In contrast, we showed previously that the single-copy genes for three other snRNAs (snR3, snR4, and snR10) are not required for viability, although cells lacking snR10 are growth impaired at low temperature. None of these RNAs associates with the Sm antigen. To assess this apparent correlation, we cloned and sequenced the genes encoding three additional non-Sm snRNAs. Comparison of these genes with nine additional yeast snRNA genes revealed a highly conserved TATA box located 92 +/- 8 nucleotides 5' of the transcriptional start site. By using the technique of gene replacement with null alleles, each of these three single copy genes was shown to be completely dispensable. We constructed multiple mutants to test the hypothesis that, individually, each of these snRNAs is nonessential because the snRNAs play functionally overlapping roles. A mutant lacking five snRNAs (snR3, snR4, snR5, snR8, snR9) was indistinguishable from the wild type, and growth of the sextuple mutant was no more impaired than that in strains lacking only snR10. This widespread dispensability of snRNAs was completely unexpected and forces us to reconsider the possible roles of these ubiquitous RNAs.


1986 ◽  
Vol 6 (11) ◽  
pp. 3990-3998
Author(s):  
S Harashima ◽  
A G Hinnebusch

GCN4 encodes a positive regulator of multiple unlinked genes encoding amino acid biosynthetic enzymes in Saccharomyces cerevisiae. Expression of GCN4 is coupled to amino acid availability by a control mechanism involving GCD1 as a negative effector and GCN1, GCN2, and GCN3 as positive effectors of GCN4 expression. We used reversion of a gcn2 gcn3 double mutation to isolate new alleles of GCD1 and mutations in four additional GCD genes which we designate GCD10, GCD11, GCD12, and GCD13. All of the mutations lead to constitutive derepression of HIS4 transcription in the absence of the GCN2+ and GCN3+ alleles. By contrast, the gcd mutations require the wild-type GCN4 allele for their derepressing effect, suggesting that each acts by influencing the level of GCN4 activity in the cell. Consistent with this interpretation, mutations in each GCD gene lead to constitutive derepression of a GCN4::lacZ gene fusion. Thus, at least five gene products are required to maintain the normal repressed level of GCN4 expression in nonstarvation conditions. Interestingly, the gcd mutations are pleiotropic and also affect growth rate in nonstarvation conditions. In addition, certain alleles lead to a loss of M double-stranded RNA required for the killer phenotype. This pleiotropy suggests that the GCD gene products contribute to an essential cellular function, in addition to, or in conjunction with, their role in GCN4 regulation.


Biomolecules ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 461 ◽  
Author(s):  
Soo Kweon Lee ◽  
Ju Hun Lee ◽  
Hyeong Ryeol Kim ◽  
Youngsang Chun ◽  
Ja Hyun Lee ◽  
...  

Cordycepin, a beneficial bioactive product specifically found in Cordyceps, has received attention in various bioindustrial applications such as in pharmaceuticals, functional foods, and cosmetics, due to its significant functions. However, low productivity of cordycepin is a barrier to commercialization. In this study, Cordyceps militaris was mutated by UV irradiation to improve the cordycepin production. The highest producer KYL05 strain was finally selected and its cordycepin production was increased about 1.5-fold compared to wild type. In addition, the effects of culture conditions were fundamentally investigated. Optimal conditions were as follows: pH 6, temperature of 25 °C, shaking speed of 150 rpm, and culture time of 6 days. Effects of medium component on cordycepin production were also investigated by using various carbon and nitrogen sources. It was found that glucose and casein hydrolysate (CH) were most effective as carbon and nitrogen sources in cordycepin production (2.3-fold improvement) with maximum cordycepin production of about 445 mg/L. In particular, production was significantly affected by CH. These results should be of value in improving the efficiency of mass production of cordycepin.


2000 ◽  
Vol 68 (2) ◽  
pp. 429-436 ◽  
Author(s):  
Renee M. Green ◽  
Anjali Seth ◽  
Nancy D. Connell

ABSTRACT Oligopeptides play important roles in bacterial nutrition and signaling. Using sequences from the available genome database forMycobacterium tuberculosis H37Rv, the oligopeptide permease operon (oppBCDA) of Mycobacterium bovis BCG was cloned from a cosmid library. An opp mutant strain was constructed by homologous recombination with an allele ofoppD interrupted by kanamycin and streptomycin resistance markers. The deletion was complemented with a wild-type copy of theopp operon. Two approaches were taken to characterize the peptide transporter defect in this mutant strain. First, growth of wild-type and mutant strains was monitored in media containing a wide variety of peptides as sole source of carbon and/or nitrogen. Among 25 peptides ranging from two to six amino acids in length, none was capable of supporting measurable growth as the sole carbon source in either wild-type or mutant strains. The second approach exploited the resistance of permease mutants to toxic substrates. The tripeptide glutathione (γ-glutamyl-l-cyteinylglycine [GSH]) is toxic to wild-type BCG and was used successfully to characterize peptide uptake in the opp mutant. In 2 mM GSH, growth of the wild-type strain is inhibited, whereas the opp mutant is resistant to concentrations as high as 10 mM. Similar results were found with the tripeptide S-nitrosoglutathione (GSNO), thought to be a donor of NO in mammalian cells. Using incorporation of [3H]uracil to monitor the effects of GSH and GSNO on macromolecular synthesis in growing cells, it was demonstrated that theopp mutant is resistant, whereas the wild type and the mutant complemented with a wild-type copy of the operon are sensitive to both tripeptides. In uptake measurements, incorporation of [3H]GSH is reduced in the mutant compared with wild type and the complemented mutant. Finally, growth of the three strains in the tripeptides suggests that GSH is bacteriostatic, whereas GSNO is bacteriocidal.


2003 ◽  
Vol 185 (16) ◽  
pp. 4672-4682 ◽  
Author(s):  
Shruti Haralalka ◽  
Suvobroto Nandi ◽  
Rupak K. Bhadra

ABSTRACT The relA gene product determines the level of (p)ppGpp, the effector nucleotides of the bacterial stringent response that are also involved in the regulation of other functions, like antibiotic production and quorum sensing. In order to explore the possible involvement of relA in the regulation of virulence of Vibrio cholerae, a relA homolog from the organism (relA VCH) was cloned and sequenced. The relA VCH gene encodes a 738-amino-acid protein having functions similar to those of other gram-negative bacteria, including Escherichia coli. A ΔrelA::kan allele was generated by replacing ∼31% of the open reading frame of wild-type relA of V. cholerae El Tor strain C6709 with a kanamycin resistance gene. The V. cholerae relA mutant strain thus generated, SHK17, failed to accumulate (p)ppGpp upon amino acid deprivation. Interestingly, compared to the wild type, C6709, the mutant strain SHK17 exhibited significantly reduced in vitro production of two principal virulence factors, cholera toxin (CT) and toxin-coregulated pilus (TCP), under virulence gene-inducing conditions. In vivo experiments carried out in rabbit ileal loop and suckling mouse models also confirmed our in vitro results. The data suggest that (p)ppGpp is essential for maximal expression of CT and TCP during in vitro growth, as well as during intestinal infection by virulent V. cholerae. Northern blot and reverse transcriptase PCR analyses indicated significant reduction in the transcript levels of both virulence factors in the relA mutant strain SHK17. Such marked alteration of virulence phenotypes in SHK17 appears most likely to be due to down regulation of transcript levels of toxR and toxT, the two most important virulence regulatory genes of V. cholerae. In SHK17, the altered expression of the two outer membrane porin proteins, OmpU and OmpT, indicated that the relA mutation most likely affects the ToxR-dependent virulence regulatory pathway, because it had been shown earlier that ToxR directly regulates their expression independently of ToxT.


2003 ◽  
Vol 16 (6) ◽  
pp. 545-552 ◽  
Author(s):  
Donghui Li ◽  
Alison M. Ashby ◽  
Keith Johnstone

Recent evidence has suggested that cutinase is required for cuticular penetration and, therefore, is essential for pathogenicity of Pyrenopeziza brassicae, the causal organism of light leaf spot disease of oilseed rape and other brassicas. In order to acquire molecular evidence for the role of cutinase in pathogenesis, the single-copy P. brassicae cutinase gene Pbc1 was disrupted by a transformation-mediated approach. Southern hybridization analysis revealed that in one mutant, NH10-1224, the disruption was due to a tandem insertion of two copies of the disruption vector into the 5′ coding region of Pbc1. In contrast to the wild type, no expression of Pbc1 was detected during in planta growth or in cutin-induced mycelium of NH10-1224 and no cutinase activity was detected in culture supernatants from NH10-1224 using pnitrophenyl butyrate as substrate. Scanning electron microscopy of Brassica napus cotyledons infected with wild-type P. brassicae confirmed that entry into the host is by direct penetration of the cuticle. In contrast, the cutinase-deficient mutant NH10-1224 failed to penetrate the cuticular layer and was unable to develop disease symptoms. This evidence is consistent with the hypothesis that Pbc1 is required for P. brassicae to penetrate the plant cuticle. Demonstration that complementation of NH10-1224 with the Pbc1 wild-type gene restores both cutinase activity and pathogenicity will be required to definitively establish that cutinase is required for successful pathogenesis of brassicas by P. brassicae.


2003 ◽  
Vol 99 (3) ◽  
pp. 678-684 ◽  
Author(s):  
Koichi Nishikawa ◽  
Neil L. Harrison

Background Previous studies have shown that specific amino acid residues in the putative second transmembrane segment (TM2) of the gamma-aminobutyric acid receptor type A (GABAA) receptor play a critical role in the enhancement of GABAA receptor function by halothane, enflurane, and isoflurane. However, very little is known about the actions of sevoflurane and desflurane on recombinant GABAA receptors. The aim of this study was to examine the effects of sevoflurane and desflurane on potentiation of GABA-induced responses in the wild-type GABAA receptor and in receptors mutated in TM2 of the alpha1, alpha 2, or beta 2 subunits. Methods GABAA receptor alpha 1 or alpha 2, beta 2 or beta 3, and gamma 2s subunit cDNAs were expressed for pharmacologic study by transfection of human embryonic kidney 293 cells and assayed using the whole cell voltage clamp technique. Concentration-response curves and EC50 values for agonist were determined in the wild-type alpha 1 beta 2 gamma 2s and alpha 2 beta 3 gamma 2s receptors, and in receptors harboring mutations in TM2, such as alpha1(S270W)beta 2 gamma 2s, alpha 1 beta 2(N265W)gamma 2s, and alpha2(S270I)beta 3 gamma 2s. The actions of clinically relevant concentration of volatile anesthetics (isoflurane, sevoflurane, and desflurane) on GABA activated Cl- currents were compared in the wild-type and mutant GABAA receptors. Results Both sevoflurane and desflurane potentiated submaximal GABA currents in the wild-type GABAA alpha 1 beta 2 gamma 2s receptor and alpha 2 beta 3 gamma 2s receptor. Substitution of Ser270 in TM2 of the alpha subunit by a larger amino acid, tryptophan (W) or isoleucine (I), as in alpha1(S270W)beta 2 gamma 2s and alpha 2(S270I)beta 3 gamma 2s, completely abolished the potentiation of GABA-induced currents by these anesthetic agents. In contrast, mutation of Asn265 in TM2 of the beta subunit to tryptophan (W) did not prevent potentiation of GABA-induced responses. The actions of sevoflurane and desflurane in the wild-type receptor and in mutated receptors were qualitatively and quantitatively similar to those observed for isoflurane. Conclusions Positions Ser270 of the GABAA alpha1 and alpha2 subunits, but not Asn265 in the TM2 of the beta2 subunit, are critical for regulation of the GABAA receptor by sevoflurane and desflurane, as well as isoflurane, consistent with the idea that these three volatile anesthetics share a common site of actions on the alpha subunit of the GABAA receptor.


Microbiology ◽  
2010 ◽  
Vol 156 (5) ◽  
pp. 1303-1312 ◽  
Author(s):  
Vijay K. Sharma ◽  
Shawn M. D. Bearson ◽  
Bradley L. Bearson

Quorum-sensing (QS) signalling pathways are important regulatory networks for controlling the expression of genes promoting adherence of enterohaemorrhagic Escherichia coli (EHEC) O157 : H7 to epithelial cells. A recent study has shown that EHEC O157 : H7 encodes a luxR homologue, called sdiA, which upon overexpression reduces the expression of genes encoding flagellar and locus of enterocyte effacement (LEE) proteins, thus negatively impacting on the motility and intimate adherence phenotypes, respectively. Here, we show that the deletion of sdiA from EHEC O157 : H7 strain 86-24, and from a hha (a negative regulator of ler) mutant of this strain, enhanced bacterial adherence to HEp-2 epithelial cells of the sdiA mutant strains relative to the strains containing a wild-type copy of sdiA. Quantitative reverse transcription PCR showed that the expression of LEE-encoded genes ler, espA and eae in strains with the sdiA deletions was not significantly different from that of the strains wild-type for sdiA. Similarly, no additional increases in the expression of LEE genes were observed in a sdiA hha double mutant strain relative to that observed in the hha deletion mutant. While the expression of fliC, which encodes flagellin, was enhanced in the sdiA mutant strain, the expression of fliC was reduced by several fold in the hha mutant strain, irrespective of the presence or absence of sdiA, indicating that the genes sdiA and hha exert opposing effects on the expression of fliC. The strains with deletions in sdiA or hha showed enhanced expression of csgA, encoding curlin of the curli fimbriae, with the expression of csgA highest in the sdiA hha double mutant, suggesting an additive effect of these two gene deletions on the expression of csgA. No significant differences were observed in the expression of the genes lpfA and fimA of the operons encoding long polar and type 1 fimbriae in the sdiA mutant strain. These data indicate that SdiA has no significant effect on the expression of LEE genes, but that it appears to act as a strong repressor of genes encoding flagella and curli fimbriae, and the alleviation of the SdiA-mediated repression of these genes in an EHEC O157 : H7 sdiA mutant strain contributes to enhanced bacterial motility and increased adherence to HEp-2 epithelial cells.


2001 ◽  
Vol 183 (2) ◽  
pp. 528-535 ◽  
Author(s):  
Hsien-Ming Lee ◽  
Shiaw-Wei Tyan ◽  
Wei-Ming Leu ◽  
Ling-Yun Chen ◽  
David Chanhen Chen ◽  
...  

ABSTRACT The xps gene cluster is required for the second step of type II protein secretion in Xanthomonas campestrispv. campestris. Deletion of the entire gene cluster caused accumulation of secreted proteins in the periplasm. By analyzing protein abundance in the chromosomal mutant strains, we observed mutual dependence for normal steady-state levels between the XpsL and the XpsM proteins. The XpsL protein was undetectable in total lysate prepared from thexpsM mutant strain, and vice versa. Introduction of the wild-type xpsM gene carried on a plasmid into thexpsM mutant strain was sufficient for reappearance of the XpsL protein, and vice versa. Moreover, both XpsL and XpsM proteins were undetectable in the xpsN mutant strain. They were recovered either by reintroducing the wild-type xpsNgene or by introducing extra copies of wild-type xpsL orxpsM individually. Overproduction of wild-type XpsL and -M proteins simultaneously, but not separately, in the wild-type strain of X. campestris pv. campestris caused inhibition of secretion. Complementation of an xpsL orxpsM mutant strain with a plasmid-borne wild-type gene was inhibited by coexpression of XpsL and XpsM. The presence of the xpsN gene on the plasmid along with thexpsL and the xpsM genes caused more severe inhibition in both cases. Furthermore, complementation of thexpsN mutant strain was also inhibited. In both the wild-type strain and a strain with the xps gene cluster deleted (XC17433), carrying pCPP-LMN, which encodes all three proteins, each protein coprecipitated with the other two upon immunoprecipitation. Expression of pairwise combinations of the three proteins in XC17433 revealed that the XpsL-XpsM and XpsM-XpsN pairs still coprecipitated, whereas the XpsL-XpsN pair no longer coprecipitated.


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