Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression of beta-galactosidase by Bacillus subtilis strains carrying transcriptional fusions of the glnA promoter region to the Escherichia coli lacZ gene was found to be regulated by the nitrogen source in glnA+ strains. The pattern of regulation was the same as that for glutamine synthetase (GS); the strongest repression was seen when glutamine was present in the medium. To see this regulation it was necessary for the fusion to be in low copy number, a condition achieved by forcing integration into the chromosome. We constructed a strain carrying a deletion mutation (glnA200) that removes part of the 5' end of the glnA structural gene. This strain did not produce any detectable GS activity or measurable GS antigen. We introduced this mutation and other glnA mutations (glnA73, glnA93, and glnA100) into strains carrying glnA-lacZ fusions. When the strains were grown with glutamine as the nitrogen source, beta-galactosidase activity was found to be derepressed. These results indicate that functional glnA gene product is required for the regulation of transcription from the glnA promoter. This supports the conclusion of our previous studies of the B. subtilis glnA gene cloned in E. coli. Additional factors may also be involved in glnA control. In particular, our results suggest that a 500-base-pair sequence of DNA between the promoter region and the start of the glnA structural gene plays a role in regulation; strains carrying this region within the glnA-lacZ fusion and unable to produce functional GS exhibited only partially derepressed beta-galactosidase levels when grown in the presence of glutamine.
 ...
PMID:Altered regulation of the glnA gene in glutamine synthetase mutants of Bacillus subtilis. 287 28

The guaC gene encodes GMP reductase, which converts GMP to inosine monophosphate. Regulation of guaC expression was examined by use of guaC-lac fusions created by Mu d1(lac). In these strains, beta-galactosidase is induced by guanine derivatives, and this induction is prevented by adenine. Our previous implication that glutamine acts as a negative effector of transcription was confirmed by showing that glutamine analogs (diazo-oxo-norleucine and methionine sulfoximine) can also induce beta-galactosidase. GMP was implicated as a likely candidate for the in vivo inducer by introducing a gpt block to prevent the conversion of guanine to GMP and a deoD block to prevent the interconversion of guanine and guanosine. Regulatory mutants were isolated by growth on lactose plus adenine. Though these showed high constitutive levels of beta-galactosidase, they were normal for the regulation of GMP reductase when the fusion was corrected by transduction to guaC+ or when guaC+ was introduced by plasmid complementation. The regulatory mutants were linked to guaC.
 ...
PMID:Regulation of guaC expression in Escherichia coli. 299 79

Titrimetric addition of hypochlorous acid (HOCl) or chloramine (NH2Cl) to suspensions of Escherichia coli decreases their ability to accumulate 14C-labeled glutamine, proline, thiomethylgalactoside, and leucine in a manner that approximately coincides with loss of cell viability; quantitative differences in cellular response are observed with the two oxidants. Inhibition of beta-galactosidase activity in E. coli ML-35, a strain lacking functional lactose permease, is complex and also depends upon the identity of the oxidant. Membrane proton conductivities and glycerol permeabilities are unchanged by addition of HOCl or NH2Cl in excess of that required for inactivation. The combined results are interpreted to indicate that the locus of HOCl attack is the cell envelope, that HOCl inactivation does not occur by loss of membrane structural integrity, that loss of transport function can be identified with either selective oxidative inhibition of the transport proteins or loss of cellular metabolic energy, and that different mechanisms of inactivation may exist for HOCl and NH2Cl.
 ...
PMID:Effects of the putative neutrophil-generated toxin, hypochlorous acid, on membrane permeability and transport systems of Escherichia coli. 301 36

The authors presented the results of a study of enzymuria (cholinesterase, gamma-glutamine transferase, alkaline phosphatase, beta-galactosidase and lactate dehydrogenase with separate determination of N- and M-subunits) in 20 patients with a mixed form of glomerulonephritis (GN), 36 with the nephrotic form of GN and 13 patients with the hematuric form of GN. The clinical importance of the determination of enzymatic activity in the urine in GN of children lies in the recognition of the degree of damage of the glomerular filter as well as the nephrothelium. Basing on enzymuria pathophysiological syndromes found in various combinations in the above forms of GN were identified. Three degrees of damage of the permeability of the glomerular filter were defined for high molecular proteins. Differences in individual values of the activity of some enzymes gave rise to differential-diagnostic coefficients as well as differential-diagnostic tables which could be used for differential diagnosis between the GN mixed and nephrotic forms.
 ...
PMID:[Clinical significance of enzymuria in glomerulonephritis in children]. 376 57

Fifty-six amber mutations of the beta-galactosidase gene of Escherichia coli were suppressed by crossing into a stock containing the supD suppressor gene. The resultant enzymes, differing only in the position of the inserted serine, were tested for stability at 57 C. Most of the suppressed enzymes were either as stable to heat as the normal enzyme or very unstable. Tests of enzymes produced by the action of other suppressors showed that the degree of stability was characteristic of a particular position in the polypeptide chain of the amino acid substitution and independent of the amino acid inserted. The mutations were placed in linear order in the gene by deletion mapping and three-point linkage tests. The consequent order of the serine substitutions disclosed an alternating pattern of stable and unstable regions over the amino-terminal two-thirds of the enzyme; the carboxy-terminal third of the enzyme was generally unstable. Considerations of coding relations and enzyme structure suggested that serine and glutamine suppression usually result in a change in the hydrophilic nature of the side chains on the outside of the enzyme molecule. It was shown that the potentially unstable regions of the enzyme are probably not indicative of stretches of alpha-helix or of sites of association. The apparent position of the substrate binding sites was correlated with the location of some of the potentially unstable regions, which may mark the parts of the polypeptide chain in proximity with the substrate.
 ...
PMID:Genetic and enzymatic experiments relating to the tertiary structure of beta-galactosidase. 488 5

Ribosomal protein methylation has been well documented but its function remains unclear. We have examined this phenomenon using an Escherichia coli mutant (prmB2), which fails to methylate glutamine residue number 150 of ribosomal protein L3. This mutant exhibits a cold-sensitive phenotype: its growth rate at 22 degrees C is abnormally low in complete medium. In addition, strains with this mutation accumulate abnormal and unstable ribosomal particles; 50-S and 30-S subunits are formed, but at a lower rate. Once assembled, ribosomes with unmethylated L3 are fully active by several criteria. (a) Protein synthesis in vitro with purified 70-S prmB2 ribosomes is as active as wild-type using either a natural (R17) or an artificial [poly(U)] messenger. (b) The induction of beta-galactosidase in vivo exhibits normal kinetics and the enzyme has a normal rate of thermal denaturation. (c) These ribosomes are standard when exposed in vitro to a low magnesium concentration or increasing molarities of LiCl. Efficient methylation of L3 in vitro requires either unfolded ribosomes or a mixture of ribosomal protein and RNA. We suggest that the L3-specific methyltransferase may qualify as one of the postulated 'assembly factors' of the E. coli ribosome.
 ...
PMID:Cold-sensitive ribosome assembly in an Escherichia coli mutant lacking a single methyl group in ribosomal protein L3. 617 16

A 1.6-kilobase-pair DNA fragment derived from the Escherichia coli chromosome was analyzed by Tn3 transposon insertion and deletion mapping to locate a mutator gene, dnaQ (mutD), and the rnh gene that codes for RNase H. When a strong promoter, PL of lambda phage, was placed at the right- and left-side of the cloned DNA fragment, the dnaQ protein and RNase H, respectively were overproduced. These results suggested that the two genes are transcribed in opposite directions and that their promoters are located in a narrow region between the genes. Nucleotide sequence analysis confirmed this and further revealed that transcriptional and translational initiation signals for the two genes overlap. From the sequence data it was deduced that the dnaQ protein and RNase H consist of 243 and 155 triplets and have molecular weights of 27,500 and 17,500, respectively. dnaQ81 amber mutant showed two codon alterations, CAG(glutamine-195) leads to TAG(amber) and ACA(threonine-193) leads to ATA(isoleucine). The dnaQ-lacZ and the rnh-lacZ fused genes were constructed and hybrid proteins with beta-galactosidase activity were produced. From beta-galactosidase levels it was estimated that the promoter for dnaQ is 5 times more active than that for rnh.
 ...
PMID:Structure and expression of the dnaQ mutator and the RNase H genes of Escherichia coli: overlap of the promoter regions. 631 47

We have isolated mutations in the Escherichia coli glnS gene encoding glutaminyl-tRNA synthetase [GlnS; L-glutamine:tRNAGln ligase (AMP-forming), EC 6.1.1.18] that give rise to gene products with altered specificity for tRNA and are designated "mischarging" enzymes. These were produced by nitrosoguanine mutagenesis of the glnS gene carried on a transducing phage (lambda pglnS+). We then selected for mischarging of su+3 tRNATyr with glutamine by requiring suppression of a glutamine-requiring beta-galactosidase amber mutation (lacZ1000). Three independently isolated mutants (glnS7, glnS8, and glnS9) were characterized by genetic and biochemical means. The enzymes encoded by glnS7, glnS8, and glnS9 appear to be highly selective for su+3 tRNATyr, because in vivo mischarging of other amber suppressor tRNAs was not detected. The GlnS mutants described here retain their capacity to correctly aminoacylate tRNAGln. All three independently isolated mutant genes encode proteins with isoelectric points that differ from those of the wild-type enzyme but are identical to each other. This suggests that only a single site in the enzyme structure is altered to give the observed mischarging properties. In vitro aminoacylation reactions with purified GlnS7 protein show that this enzyme can also mischarge some tRNA species lacking the amber anticodon. This is an example of mischarging phenotype conferred by a mutation in an aminoacyl-tRNA synthetase gene; the results are discussed in the context of earlier genetic studies with mutant tRNAs.
 ...
PMID:Transfer RNA mischarging mediated by a mutant Escherichia coli glutaminyl-tRNA synthetase. 638 58

Derepression of nitrogen fixation (nif) genes in Klebsiella pneumoniae following transfer from NH+4-sufficiency to N-free medium was preceded by rapid expansion of the guanosine 5'-diphosphate 3'-diphosphate (ppGpp) pool. When derepressed in N-free medium supplemented with glutamine (600 micrograms ml-1), expression from the nifH and nifL promoters, determined as beta-galactosidase activity in nif::lac merodiploid strains, was stimulated 7-fold and nitrogenase activity 26-fold; ppGpp did not accumulate, remaining at the levels found in NH+4-repressed populations. The relaxed mutant K. pneumoniae relA40, which accumulates only very low levels of ppGpp, showed partial derepression of nitrogenase activity in the presence of glutamine, thus ppGpp is unlikely to be an effector of nif expression. ATP and GTP levels were elevated under conditions where nif expression was enhanced, consistent with previous data suggesting that maintenance of ATP levels is a prerequisite for the expression of nif genes in K. pneumoniae.
 ...
PMID:Nitrogenase synthesis in Klebsiella pneumoniae: enhanced nif expression without accumulation of guanosine 5'-diphosphate 3'-diphosphate. 639 16

A purE::lac fusion strain was isolated by using a special Mu phage developed by M. Casadaban. In the presence of adenine (100 micrograms/ml), beta-galactosidase synthesis was repressed by greater than 90%. beta-Galactosidase activity could be detected 6 to 8 min after the removal of adenine and increased linearly for at least 20 min. purR- mutants were isolated and synthesized 1.7- to 1.8-fold-higher levels of beta-galactosidase compared with purR+ cells. Azaserine derepressed purE transcription approximately 1.7-fold by lowering purine nucleotide pools. Glutamine and pyrimidine supplementation or starvation had no effect on purE transcription. A comparison of the rate of de novo purine biosynthesis and purE transcription indicated that the in vivo rate of de novo purine biosynthesis was more sensitive to the inhibitory effects of adenine than was transcription at the purE locus.
 ...
PMID:Regulation of purE transcription in a purE::lac fusion strain of Escherichia coli. 703 38


<< Previous 1 2 3 4 Next >>