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

The requirements for efficient translation termination are incompletely understood. Since the local context surrounding stop codons can influence the efficiency of translation termination, premature termination codons introduced by random mutation may not always terminate at the optimal efficiencies expected of naturally occurring stop codons. To investigate whether this could result in physiologically significant levels of read through, we examined the suppression of premature translation termination mutations within a sequence motif of the yeast Ste6 protein (Ste6p) that is highly conserved among members of the ATP-binding cassette (ABC) transporter family. The human cystic fibrosis transmembrane conductance regulator (CFTR), which is defective in individuals with the disease cystic fibrosis, is also a member of this protein family. The mutations examined in Ste6p were chosen because a premature termination codon at the corresponding residue of CFTR has previously been reported to cause less severe pulmonary involvement than some missense mutations, suggesting that low level suppression of this stop codon could be occurring. Our results indicate that these premature stop codons in Ste6p can be suppressed at frequencies as high as 10%. Characterization of this phenomenon using a beta-galactosidase read through assay system showed that a limited sequence context surrounding this site contained information that was sufficient to cause suppression of translation termination. Amino acid sequence analysis of the full-length translation products produced by read through of an amber codon demonstrated that termination suppression was mediated by near-cognate tRNA mispairing that resulted in the insertion of tyrosine, lysine, or tryptophan.
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PMID:Premature translation termination mutations are efficiently suppressed in a highly conserved region of yeast Ste6p, a member of the ATP-binding cassette (ABC) transporter family. 751 33

A conserved Aeromonas salmonicida gene (abcA) affecting expression of the surface array protein gene (vapA) in Escherichia coli was identified. The 924-bp gene starts 205 bp after vapA and codes for a protein with a deduced molecular weight (M(r)) of 34,015 containing an N-terminal P-loop and significant homology to the ATP-binding cassette transport protein superfamily. AbcA was identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) by using T7 polymerase expression and DNA-directed translation and was copurified with the sarkosyl-soluble cytoplasmic membrane fraction. The protein displayed aberrant migration during SDS-PAGE. A lacZ fusion containing 128 bp of upstream sequence and 387 bases in the 5' end of abcA was constructed, and the beta-galactosidase activity of the abcA-lacZ fusion gene was shown to be similar in E. coli and A. salmonicida. The 130,000-M(r) AbcA-LacZ fusion protein was purified, and by using an ATP affinity column, the 129 AbcA N-terminal P-loop-containing residues were shown to bind ATP.
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PMID:An Aeromonas salmonicida gene which influences a-protein expression in Escherichia coli encodes a protein containing an ATP-binding cassette and maps beside the surface array protein gene. 849 26

The Escherichia coli ProU system is a member of the ATP-binding cassette (ABC) superfamily of transporters. ProU consists of three components (ProV, ProW, and ProX) and functions as a high-affinity, binding protein-dependent transport system for the osmoprotectants glycine betaine and proline betaine. The ProW protein is the integral inner membrane component of the ProU system. Its hydropathy profile predicts seven transmembrane spans and a hydrophilic amino terminus of approximately 100 residues, and it suggests the presence of an amphiphilic alpha-helix (L-61 to F-97) in close proximity to the first strongly hydrophobic segment of ProW. We have studied the membrane topology of the ProW protein by the phoA and lacZ gene fusion approach. A collection of 10 different proW-phoA fusions with alkaline phosphatase activity and 8 different proW-lacZ fusions with beta-galactosidase activity were isolated in vivo after TnphoAB and TnlacZ mutagenesis of a plasmid-encoded proW gene. The recovery of both enzymatically active ProW-PhoA and ProW-LacZ hybrid proteins indicates that segments of ProW are exposed on both sides of the cytoplasmic membrane. To compare the enzymatic activities of each of the indicator proteins joined at a particular site in ProW, we switched the phoA and lacZ reporter genes in vitro in each of the originally in vivo-isolated gene fusions. A mirror-like pattern in the enzyme activity of the resulting new ProW-PhoA and ProW-LacZ hybrid proteins emerged, thus providing positive signals for the location of both periplasmic and cytoplasmic domains in ProW. The protease kallikrein digests the amino-terminal tail of a ProW-LacZ hybrid protein in spheroplasts, suggesting that the amino terminus of ProW is located on the periplasmic side of the cytoplasmic membrane. From these data, a two-dimensional model for ProW was constructed; this model consists of seven transmembrane alpha-helices and an unusual amino-terminal tail of approximately 100 amino acid residues that protrudes into the periplasmic space.
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PMID:Use of phoA and lacZ fusions to study the membrane topology of ProW, a component of the osmoregulated ProU transport system of Escherichia coli. 880 24

Multidrug resistance (MDR) mediated by broad specificity transporters is one of the most important strategies used by pathogens, including cancer cells, to evade chemotherapy. In the yeast Saccharomyces cerevisiae, a complex pleiotropic drug resistance (PDR) network of genes involved in MDR is composed of the transcriptional regulators Pdr1p and Pdr3p, which activate expression of the ATP-binding cassette (ABC) MDR transporters-encoding genes PDR5, SNQ2, and YOR1 as well as other not yet identified genes. We have screened 349 toxic compounds in isogenic S. cerevisiae strains deleted of PDRS, SNQ2, or YOR1 in different combinations as well as both PDR1 and PDR3. The screen revealed extremely promiscuous, yet limited, and to a large extent overlapping but distinct drug resistance profiles of Pdr5p, Snq2p, and Yor1p. These ABC-MDR transporters mediated resistance to most currently available classes of clinically and agriculturally important fungicides and also to many antibiotics, herbicides, and others. Several classes of compounds were identified for the first time in the drug resistance spectrum of MDR transporters. These are fungicides, such as anilinopyrimidines, benzimidazoles, benzenedicarbonitriles, dithiocarbamates, guanidines, imidothiazoles, polyenes, pyrimidynyl carbinols, and strobilurine analogues; the urea derivative and anilide herbicides; flavonoids, several membrane lipids resembling detergents; and newly synthesized lysosomotropic aminoesters; as well as many others. Identification of compounds showing Pdr1p, Pdr3p-dependent, but Pdr5p-, Snq2p-, and Yor1p-independent toxicity, reflected in the case of rhodamine 6G, by efflux alterations, suggests the involvement of new drug resistance genes and is a first step toward their identification. The highly increased toxicity of bile acids toward the PDR1, PDR3 double disruptant together with the decreased level of BAT1 promoter dependent beta-galactosidase activity suggest that the Bat1p ABC transporter is a new member of the PDR network. Our results may contribute to a better understanding of the mechanism of MDR, in particular in the pathogenic yeast Candida albicans. They also provide and indication of the physiological function of MDR transporters and suggest new approaches for the cloning of the mammalian bile acid transporters.
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PMID:In vivo characterization of the drug resistance profile of the major ABC transporters and other components of the yeast pleiotropic drug resistance network. 981 66

Many non-lantibiotic bacteriocins of lactic acid bacteria are produced as precursors with N-terminal leader peptides different from those present in preproteins exported by the general sec-dependent (type II) secretion pathway. These bacteriocins utilize a dedicated (type I) secretion system for externalization. The secretion apparatus for the lactococcins A, B, and M/N (LcnA, B, and M/N) from Lactococcus lactis is composed of the two membrane proteins LcnC and LcnD. LcnC belongs to the ATP-binding cassette transporters, whereas LcnD is a protein with similarities to other accessory proteins of type I secretion systems. This paper shows that the N-terminal part of LcnC is involved in the processing of the precursor of LcnA. By making translational fusions of LcnC to the reporter proteins beta-galactosidase (LacZ) and alkaline phosphatase (PhoA*), it was shown that both the N- and C-terminal parts of LcnC are located in the cytoplasm. As the N terminus of LcnC is required for LcnA maturation and is localized in the cytoplasm, we conclude that the processing of the bacteriocin LcnA to its mature form takes place at the cytosolic side of the cytoplasmic membrane.
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PMID:Membrane topology of the lactococcal bacteriocin ATP-binding cassette transporter protein LcnC. Involvement of LcnC in lactococcin a maturation. 1008 80

A yeast two-hybrid screen searching for chromosomally encoded proteins that interact with the Agrobacterium tumefaciens VirB8 protein was carried out. This screen identified an interaction candidate homologous to the partial sequence of a gene that had previously been identified in a transposon screen as a potential regulator of virG expression, chvD. In this report, the cloning of the entire chvD gene is described and the gene is sequenced and characterized. Insertion of a promoterless lacZ gene into the chvD locus greatly attenuated virulence and vir gene expression. Compared to that of the wild-type strain, growth of the chvD mutant was reduced in rich, but not minimal, medium. Expression of chvD, as monitored by expression of beta-galactosidase activity from the chvD-lacZ fusion, occurred in both rich and minimal media as well as under conditions that induce virulence gene expression. The ChvD protein is highly homologous to a family of ATP-binding cassette transporters involved in antibiotic export from bacteria and has two complete Walker box motifs. Molecular genetic analysis demonstrated that disruption of either Walker A box, singly, does not inactivate this protein's effect on virulence but that mutations in both Walker A boxes renders it incapable of complementing a chvD mutant strain. Constitutive expression of virG in the chvD mutant strain restored virulence, supporting the hypothesis that ChvD controls virulence through effects on virG expression.
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PMID:ChvD, a chromosomally encoded ATP-binding cassette transporter-homologous protein involved in regulation of virulence gene expression in Agrobacterium tumefaciens. 1134 38

To understand the mechanisms of high-pH-induced protection in Sinorhizobium meliloti, a cDNA-amplified fragment length polymorphism analysis of S. meliloti cells grown in minimal medium under alkali stress was undertaken. This revealed that the first four genes of a seven-gene cluster encode the characteristic components of a putative sugar ATP-binding cassette (ABC) transporter. A functional study suggested that this putative sugar ABC transporter might play a role in potassium transport regulation, which we therefore designated supABCD. The transcription of three potassium uptake genes, trkH, kdpA and kup1, in S. meliloti is significantly attenuated in the supA mutant in the presence of potassium. The supA mutant was unable to grow at elevated levels of potassium. The expression of supA, as determined by beta-galactosidase activity, was shown to be induced by potassium but not by sodium.
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PMID:An ABC transporter is required for alkaline stress and potassium transport regulation in Sinorhizobium meliloti. 1922 Apr 74