Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.2.1.23 (beta-galactosidase)
14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The chromosomal lac region of the coliform bacterium Klebsiella M5al was cloned into the multicopy plasmid pBR322 to give pHE7 and pHE8. pHE8 contains 12.6 kb of M5al DNA, including its complete lac operon, and pHE7 contains 2.5 kb of M5al DNA and includes the complete lac Y gene and a small segment of lacZ. The M5al operon has the same gene order as the Escherichia coli lac operon. The lac genes of the Lac plasmid of Klebsiella V9A were cloned into pBR322 to give pHE1 and pHE2, of approximately 39 and 43 kb. Both plasmids were unstable in an E. coli RecA-strain, in contrast to the stability of pHE8. Polyacrylamide gel electrophoresis tests suggested that the M5al beta-galactosidase monomer is about 5% longer, i.e. has about 50 more amino acids, than that of the E. coli Z gene. Tests made on the enzymes coded by the lac operons of M5al, another Klebsiella strain (V9A) and its resident Lac plasmid, and several Lac+ Enterobacteria, led to the conclusion that only Escherichia coli among the Enterobacteria contains an active lacA gene.
...
PMID:Clonal analysis of the lac operons from Klebsiella M5al and the Lac plasmid (pRE2) from Klebsiella V9A. 251 12

Two plasmids were isolated containing oppositely oriented gamma-delta insertions between the wild-type transcription initiation site of the nifHDKY operon and the nifH coding sequence. The nifHDKY promoter of Klebsiella pneumoniae, similar to other nitrogen fixation (nif) promoters, normally requires the products of ntrA and nifA for activity. Mutations that allowed constitutive expression of the nifHDKY operon were searched for by transforming a plasmid, containing the regulatory region of this operon followed by an in-frame nifH'-'lacZ fusion, into a Lac- Escherichia coli strain (which contains no nifA) and screening for Lac+ derivatives. The plasmids described here were isolated from such derivatives and directed the constitutive expression of beta-galactosidase. Deletion analysis indicated that gamma-delta promoters other than those transcribing tnpA and tnpR were involved in this expression. Nuclease S1 mapping revealed outward-reading transcription initiation sites in both the gamma end and the delta end of the transposon. Most interestingly, one initiation site on each end was located in corresponding positions within the terminal inverted repeats. The sites were in the center of the longest sequence, of 12 bp, contiguously conserved between the terminal inverted repeats of gamma-delta and the related transposon Tn3. In gamma-delta and Tn3, this sequence has been recently implicated in transposase binding. These results suggest a possible interrelationship between transcription from the "end" promoters and transposition.
...
PMID:Outreading promoters are located at both ends of the gamma-delta transposon. 254 4

The nifA gene of Klebsiella pneumoniae, which encodes the transcriptional activator of nif gene expression, was cloned into a number of plasmid vectors to obtain high-level synthesis of nifA product (NifA). When over-produced, NifA was very insoluble and it precipitated with the cell debris after cell lysis. Localization of beta-galactosidase activity from a nifA-lacZ translational fusion confirmed the insoluble nature of NifA. Analysis of two translational fusions in which the last six C-terminal amino acids of NifA were deleted suggests that these residues are required for activity.
...
PMID:Over-production and characterization of the nifA gene product of Klebsiella pneumoniae--the transcriptional activator of nif gene expression. 284 61

Rhizobium japonicum nifH'- and nifD'-'lacZ fusions were constructed using the translational fusion vector pMC1403. beta-Galactosidase activities from these fusion plasmids were measured in wild-type, ntrA- and delta(ntrBC) Escherichia coli strains carrying plasmids which overproduced the Klebsiella pneumoniae nifA or ntrC gene products. In contrast to results reported in R. meliloti (ref. in the text) neither nifH nor nifD promoters were activated by the ntrC product. In the presence of nifA gene product, however, beta-galactosidase activity from both nifH and nifD fusion plasmids increased substantially. NifA-mediated activation of these Rhizobium promoters was temperature sensitive and was dependent on the host ntrA product. In order to determine the point at which the fusion transcripts were initiated, RNA was extracted from the wild-type E. coli strain carrying each of the R. japonicum fusion plasmids plus the nifA overproducing plasmid. This RNA was used to perform S1 mapping experiments. NifA-mediated transcription from both R. japonicum promoters, began at the same point as previously determined in soybean root-nodule bacteroids (ref. in the text). The results obtained suggest that there may be differences in the mode of regulation between members of the fast- and slow-growing rhizobia. Also, the results of the S1 mapping experiments indicate that activation of the R. japonicum nitrogenase structural genes may be similar to the activation of nif genes in K. pneumoniae thus raising the possibility that R. japonicum may contain nifA and ntrA-like genes.
...
PMID:Expression of Rhizobium japonicum nifH and nifDK operons can be activated by the Klebsiella pneumonia nifA protein but not by the product of ntrC. 286 69

Nine single C-to-T transitions were introduced into the -26 to -12 region of the Klebsiella pneumoniae nifL promoter by bisulphite mutagenesis of M13 heteroduplexes containing a 15 nucleotide single-stranded loop. Mutant promoter fragments were inserted into translational lac fusion vectors to utilise beta-galactosidase activity as a measure of promoter efficiency. Mutations in invariant nucleotides found in the consensus sequence for nif promoters gave a strong 'down' promoter phenotype with respect to transcriptional activation. Mutations in semi-conserved residues had a much weaker down phenotype, whereas a mutation which increased homology to the consensus sequence enhanced promoter strength. One mutant showed increased activation by ntrC and decreased activation by nifA.
...
PMID:Deletion loop mutagenesis of the nifL promoter from Klebsiella pneumoniae: role of the -26 to -12 region in promoter function. 302 13

Plasmids containing hybrid genes, in which different Klebsiella pneumoniae nif (nitrogen-fixation) promoters were fused with the structural part of the Escherichia coli lac operon, were introduced into a double auxotrophic derivative of Agrobacterium tumefaciens C58. A study of their expression in the new host was made simple by the inherent inability of A. tumefaciens C58 to produce beta-galactosidase unless provided with the wild-type lac operon of E. coli. As shown by quantitative measurements of the enzyme, all K. pneumoniae promoters were expressed well in A. tumefaciens C58, even under conditions known to repress them. It also has been shown that the activity of K. pneumoniae nif A is essential for the expression of nifHDK even when introduced into A. tumefaciens. After entering the new host the plasmids, the nif genes and the fusion alleles contained in them, remained stable. Possible mechanisms responsible for the constitutive behaviour of nif promoters in A. tumefaciens are discussed.
...
PMID:Klebsiella pneumoniae nif-lac fusions are expressed in Agrobacterium tumefaciens C58. 310 28

Galactose appears to be the physiological inducer of the chromosomal lac operon in Klebsiella aerogenes. Both lactose and galactose are poor inducers in strains having a functional galactose catabolism (gal) operon, but both are excellent inducers in gal mutants. Thus the slow growth of K. aerogenes on lactose reflects the rapid degradation of the inducer. Several pts mutations were characterized and shown to affect both inducer exclusion and permanent catabolite repression. The beta-galactosidase of pts mutants cannot be induced at all by lactose, and pts mutants appear to have a permanent and constitutive inducer exclusion phenotype. In addition, pts mutants show a reduced rate of glucose metabolism, leading to slower growth on glucose and a reduced degree of glucose-mediated permanent catabolite repression. The crr-type pseudorevertants of pts mutations relieve the constitutive inducer exclusion for lac but do not restore the full level of glucose-mediated permanent catabolite repression and only slightly weaken the glucose-mediated inducer exclusion. Except for weakening the glucose-mediated permanent catabolite repression, pts and crr mutations have no effect on expression of the histidine utilization (hut) operons.
...
PMID:Regulation of the galactose-inducible lac operon and the histidine utilization operons in pts mutants of Klebsiella aerogenes. 314 52

A series of fusions between the gene for the Klebsiella pneumoniae secreted lipoprotein pullulanase (pulA) and the genes for cytoplasmic beta-galactosidase (lacZ) or periplasmic alkaline phosphatase (phoA) were created by transposon mutagenesis using mini-MudII1681 or TnphoA, respectively. The hybrid genes were expressed in Escherichia coli K-12 with or without the K. pneumoniae genes that promote pullulanase secretion in E. coli. We characterized seven different pulA-lacZ gene fusions encoding hybrid polypeptides containing from 14 to c. 1060 residues of pro-pullulanase. All but the smallest hybrid were fatty acylated and were toxic to producing cells, causing the accumulation of precursors of other exported proteins. Four different pulA-phoA gene fusions encoded hybrids with alkaline phosphatase activity. All four hybrids were fatty acylated, but were not toxic. Although the hybrids were apparently membrane-associated, they were not secreted into the medium either by E. coli carrying pullulanase secretion genes or by K. pneumoniae. Immunofluorescence tests indicated that the pullulanase secretion genes promoted the localization of one of these hybrids to the outer face of the E. coli outer membrane, which may have important implications for the design of live vaccine strains and of immobilized enzymes.
...
PMID:A gene fusion approach to the study of pullulanase export and secretion in Escherichia coli. 332 97

Sixty-three strains of E. coli transconjugants derived from E. coli K12 J62-1 containing plasmids derived from Klebsiella pneumoniae, were examined for the presence of phenotypic markers other than antibiotic resistance. This investigation was carried out using API 50CHE and API ZYM tests. Beta-glucosidase was found in 63/63 J62-1 transconjugants. Dulcitol dehydrogenase was present in 92.1% while beta-galactosidase was present in 70% of transconjugants. None of the three enzymes were present in the recipient. Dulcitol dehydrogenase was present only in the transconjugants and is absent from the donors and recipient. The transconjugants, cured of their antibiotic resistant plasmids retained dulcitol dehydrogenase activity. The Klebsiella donors were not cured of antibiotic resistance by the curing process.
...
PMID:Biochemical characterization of E. coli transconjugants with plasmids derived from Klebsiella pneumoniae. 389 56

Biological nitrogen fixation is catalyzed by nitrogenase, an enzyme complex exclusive to prokaryotes. We used the yeast Saccharomyces cerevisiae to study the synthesis, and subsequently the assembly, of nitrogenase components in a eukaryote. Here, the Klebsiella pneumoniae nifH gene, encoding the subunit of the Fe protein (Kp2) component of nitrogenase, was expressed in S. cerevisiae from the yeast ADHI promoter. The nifH gene product, detected in yeast by immunoblot analysis with anti-Kp2 antibodies, exhibited the same electrophoretic mobility in SDS-polyacrylamide gels as that of the Kp2 subunit synthesized in K. pneumoniae. Estimates of Kp2 antigen and assays of beta-galactosidase activity specified by nifH'-'lacZ fusions showed that the level of nifH product was similar in anaerobically and aerobically grown yeast, but varied with different transforming plasmids and in various haploid and diploid yeast strains. A cistron located downstream to nifH in a transcript resembling the polycistronic mRNA of the nifHDKY operon in K. pneumoniae is not translated in yeast.
...
PMID:Expression of a nitrogen-fixation gene encoding a nitrogenase subunit in yeast. 389 31


<< Previous 1 2 3 4 5 6 7 Next >>

---