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At least 487 records · Page 27Linked to original sources
PubMed1998

Separation of human globin chains by micellar electrokinetic capillary chromatography.

A new separation method of human globin chains by micellar electrokinetic capillary chromatography (MECC) is described. In this method, a 25 mM phosphate buffer (pH 2.5) containing 7 M urea and 1% (w/v) reduced Triton X-100 buffer system was used. All experiments were performed in a 47 cmx50 microm I.D. uncoated fused-silica capillary. The separation voltage was set at 19 kV. Normal globin chains derived from normal adults and newborns, alpha, beta, delta, Ggamma and Agamma globin chains as well as common variant globin chains were successfully separated within 20 min. High reproducible migration times of globin chains (CVs of intra- and inter-assay were less than 1% and 2% respectively), and quantification of Ggamma and Agamma chains (CVs for intra- and inter-assay were less than 5% and 10%, respectively) were obtained. This new MECC method provides primary information on structural modification of globin chains. It can be an important diagnostic tool in clinical laboratory practice in the field of hemoglobinopathies.

Adult↗
PubMed2002

Biochemical characterization of a membrane-bound manganese-containing superoxide dismutase from the cyanobacterium Anabaena PCC 7120.

The filamentous cyanobacterium Anabaena PCC 7120 (now renamed Nostoc PCC 7120) possesses two genes for superoxide dismutase (SOD). One is an iron-containing (FeSOD) whereas the other is a manganese-containing superoxide dismutase (MnSOD). Localization experiments and analysis of the sequence showed that the FeSOD is cytosolic, whereas the MnSOD is a membrane-bound homodimeric protein containing one transmembrane helix, a spacer region, and a soluble catalytic domain. It is localized in both cytoplasmic and thylakoid membranes at the same extent with the catalytic domains positioned either in the periplasm or the thylakoid lumen. A phylogenetic analysis revealed that generally the highly homologous MnSODs of filamentous cyanobacteria are unique in being membrane-bound. Two recombinant variants of Anabaena MnSOD lacking either the hydrophobic region (MnSOD(Delta 28)) or the hydrophobic and the linker region (MnSOD(Delta 60)) are shown to exhibit the characteristic manganese peak at 480 nm, an almost 100% occupancy of manganese per subunit, a specific activity using the ferricytochrome assay of (660 +/- 90) unit mg-1 protein and a dissociation constant for the inhibitor azide of (0.84 +/- 0.05) mm. Using stopped-flow spectroscopy it is shown that the decay of superoxide in the presence of various (MnSOD(Delta 28)) or (MnSOD(Delta 60)) concentrations is first-order in enzyme concentration allowing the calculation of catalytic rate constants which increase with decreasing pH: 8 x 10(6) m-1 s-1 (pH 10) and 6 x 10(7) m-1 s-1 (pH 7). The physiological relevance of these findings is discussed with respect to the bioenergetic peculiarities of cyanobacteria.

Amino Acid Sequence↗
PubMed1991

Primary cutaneous gamma/delta T-cell lymphoma presenting as disseminated pagetoid reticulosis.

The first case of primary gamma/delta cutaneous T-cell lymphoma (CTCL) with a fatal outcome is reported. The patient had the clinical and histopathologic features of disseminated pagetoid reticulosis, a rare form of CTCL characterized by a strong epidermotropic lymphoid infiltrate. Extensive immuno-cytochemical studies showed that the neoplastic cells were almost exclusively localized in the epidermis, expressed the gamma/delta variant of the T-cell receptor (CD3+, TCR-delta-1+) and were CD5+, CD7+, CD27+, CD29+, CD43+, CD44+, CD45+, CD45RA+, CD54+, CD69+, but beta F1-, Ti gamma a-, BB3-, A13-, CD2-, CD4-, CD8-, CD11a-, CD49d-, CD25-, CD30-, and HLA-DR-. A comparison of our results with those of the literature, which have not included gamma/delta T-cell receptor analysis, suggests that some reported cases of pagetoid reticulosis may have phenotypes similar to our case. Electron microscopy studies demonstrated that the gamma/delta T lymphocytes were villous, containing dense and multivesicular bodies, and formed close contacts with the surrounding keratinocytes, suggesting that these cells should have a role in the skin-associated lymphoid tissue. The proliferating cells in our case might represent the neoplastic counterpart of the recently reported CD2- subset of normal human peripheral blood gamma/delta T lymphocytes.

Aged↗
PubMed2002

Analysis of natural variants of the human immunodeficiency virus type 1 gag-pol frameshift stem-loop structure.

Human immunodeficiency virus type 1 uses ribosomal frameshifting for translation of the Gag-Pol polyprotein. Frameshift activities are thought to be tightly regulated. Analysis of gag p1 sequences from 270 plasma virions identified in 64% of the samples the occurrence of polymorphism that could lead to changes in thermodynamic stability of the stem-loop. Expression in Saccharomyces cerevisiae of p1-beta-galactosidase fusion proteins from 10 representative natural stem-loop variants and three laboratory mutant constructs (predicted the thermodynamic stability [Delta G degrees] ranging from -23.0 to -4.3 kcal/mol) identified a reduction in frameshift activity of 13 to 67% compared with constructs with the wild-type stem-loop (Delta G degrees, -23.5 kcal/mol). Viruses carrying stem-loops associated with greater than 60% reductions in frameshift activity presented profound defects in viral replication. In contrast, viruses with stem-loop structures associated with 16 to 42% reductions in frameshift efficiency displayed no significant viral replication deficit.

Base Sequence↗
PubMed2003

Transgenic CaMKIIdeltaC overexpression uniquely alters cardiac myocyte Ca2+ handling: reduced SR Ca2+ load and activated SR Ca2+ release.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) delta is the predominant cardiac isoform, and the deltaC splice variant is cytoplasmic. We overexpressed CaMKIIdeltaC in mouse heart and observed dilated heart failure and altered myocyte Ca2+ regulation in 3-month-old CaMKIIdeltaC transgenic mice (TG) versus wild-type littermates (WT). Heart/body weight ratio and cardiomyocyte size were increased about 2-fold in TG versus WT. At 1 Hz, twitch shortening, [Ca2+]i transient amplitude, and diastolic [Ca2+]i were all reduced by approximately 50% in TG versus WT. This is explained by >50% reduction in SR Ca2+ content in TG versus WT. Peak Ca2+ current (ICa) was slightly increased, and action potential duration was prolonged in TG versus WT. Despite lower SR Ca2+ load and diastolic [Ca2+]i, fractional SR Ca2+ release was increased and resting spontaneous SR Ca2+ release events (Ca2+ sparks) were doubled in frequency in TG versus WT (with prolonged width and duration, but lower amplitude). Enhanced Ca2+ spark frequency was also seen in TG at 4 weeks (before heart failure onset). Acute CaMKII inhibition normalized Ca2+ spark frequency and ICa, consistent with direct CaMKII activation of ryanodine receptors (and ICa) in TG. The rate of [Ca2+]i decline during caffeine exposure was faster in TG, indicating enhanced Na+-Ca2+ exchange function (consistent with protein expression measurements). Enhanced diastolic SR Ca2+ leak (via sparks), reduced SR Ca2+-ATPase expression, and increased Na+-Ca2+ exchanger explain the reduced diastolic [Ca2+]i and SR Ca2+ content in TG. We conclude that CaMKIIdeltaC overexpression causes acute modulation of excitation-contraction coupling, which contributes to heart failure.

Animals↗
PubMed1991

Multiple origins of the human glycophorin Sta gene. Identification of hot spots for independent unequal homologous recombinations.

Human glycophorin Sta (HGpSta), one of the structural variants of erythrocyte membrane sialoglycoproteins, is encoded by a delta-alpha hybrid gene that arose from a single unequal crossover between the parent HGpB(delta) and HGpA(alpha) genes. We report here the identification of two new HGpSta genes (type A and type B) in four unrelated Sta heterozygotes from two ethnic groups. These Sta genes represent distinct genetic isoforms that differ from the previously reported Sta gene (type C) in the location of crossing-over sites. Comparison of nucleotide sequences among HGpB(delta), HGpA(alpha), and HGpSta type A genes revealed that the delta-alpha unequal crossover for the Sta type A gene occurred 110-246 base pairs downstream from pseudoexon III. In the crossing-over site of this Sta gene, an AT-rich sequence lying 3' to a nonameric palindrome was found to be highly similar to the lambda phage attachment site, att B, in inverted orientation. In the Sta type B gene, the delta-alpha crossing-over point was localized to an AG-rich sequence that is 302-490 base pairs downstream from pseudoexon III. Multiple lambda chi-like elements were identified at the crossover boundaries and within the breakpoint of this Sta gene. These results suggest strongly that recurrent and independent unequal recombination events have occurred in the formation of multiple Sta genes and that particular genomic sequences are important in defining the recombination sites for these homology-driven processes.

Asian People↗
PubMed1992

Spontaneous delta- to beta-globin switching in K562 human leukemia cells.

Previous analysis of the hemoglobin phenotype of the K562 human erythroleukemia cell line showed regulated expression of the epsilon-, zeta-, gamma-, alpha-, and delta-globin genes. Expression of the beta-globin genes has not been previously detected in this cell line. In this report, we describe the isolation of a variant of the K562 cell line that actively expresses beta-globin messenger RNA (mRNA) and polypeptide and shows greatly reduced expression of the delta-globin genes. This phenotype developed spontaneously in culture while two other K562 isolates grown under the same culture conditions have not undergone the same delta- to beta-globin switch. Analysis of this unique K562 variant shows that a construct containing a beta-globin promoter is quite active upon transient transfection into these cells. This finding suggests that the activation of the endogenous beta-globin genes results from changes in the trans-acting environment of these cells. The regulation of the beta-globin genes in this variant is characterized by a paradoxical decrease in the level of beta-globin mRNA after exposure to hemin. Other globin genes of this variant are appropriately regulated and show increased expression after hemin induction. Further study of this variant may shed light on mechanisms of gene regulation that are involved in hemoglobin switching.

Gene Expression Regulation↗
PubMed1977

The frequency in Japanese of genetic variants of 22 proteins II. Carbonic anhydrase I and II, lactate dehydrogenase, malate dehydrogenase, nucleoside phosphorylase, triose phosphate isomerase, haemoglobin A and haemoglobin A2.

This paper presents the results of a survey of Japanese for electrophoretic variants of CA I, CA II, LDH, MDH, TPI, NP, HB A and A2, the number of determinations per system ranging from 738 to 4029. Four similar variants of CA I (designed CA IHIR1), one of LDH (designated LDHNGS1), one of MDH (designated MDHS 7HIR1), two of HB A (one a reascertainment of HB Hijiyama, the other not characterized), and one characterized by the absence of HB A2 (delta-thalassaemia) were observed and are described. The CA IHIR1, LDHNAG1 and MDHS 2HIR1 variants have not been previously observed in Japan. No electrophoretic variants were found in the TPI and NP systems.

Adult↗
PubMed1993

Structural features which control folding of homologous proteins in cell-free translation systems. The effect of a mitochondrial-targeting presequence on aspartate aminotransferase.

When the precursor to mitochondrial aspartate aminotransferase (pmAspAT) is synthesized in a rabbit reticulocyte lysate translation system (RRL), its properties are quite unlike those of the purified protein (Mattingly, J.R., Jr., Youssef, J., Iriarte, A., and Martinez-Carrion, M. (1993) J. Biol. Chem. 268, 3925-3937). These results suggest that molecular chaperones present in RRL modulate the folding of pmAspAT. To investigate the structural basis for this, we have used protease resistance to monitor the extent of folding for several related AspATs after synthesis in RRL and in wheat germ extract (WGE). In addition to pmAspAT, the following proteins were examined: the mature form of pmAspAT (delta 2-28 pmAspAT), its cytosolic counterpart (cAspAT), a chimeric protein consisting of the presequence of pmAspAT attached to the amino terminus of cAspAT (pcAspAT), and a pmAspAT variant in which the presequence and the amino-terminal domain of the mature enzyme are deleted (delta 2-57 pmAspAT). In RRL, delta 2-28 pmAspAT folds somewhat faster than intact pmAspAT, whereas the truncated delta 2-57 pmAspAT is unable to fold. In contrast, cAspAT and pcAspAT both fold with extreme rapidity. After synthesis in WGE, pmAspAT and delta 2-28 pmAspAT never acquire a protease-resistant conformation, whereas the folding of cAspAT and pcAspAT still occurs rapidly. We conclude that the presequence has only a minor role in determining the folding rate of the pmAspAT mitochondrial precursor protein in RRL or WGE and has no influence on the folding of the homologous cAspAT. Rather, the primary sequence of the mature part of the protein seems to dictate whether or how molecular chaperones regulate folding events.

Amino Acid Sequence↗
PubMed1993

Voltage-dependent inhibition of the sodium pump by external sodium: species differences and possible role of the N-terminus of the alpha-subunit.

Currents generated by the Na+/K+ ATPase were measured under voltage clamp in oocytes of Xenopus laevis. The dependence of pump current on external [Na+] was investigated for the endogenous Xenopus pump as well as for wild-type and mutated pumps of electroplax of Torpedo californica expressed in the oocytes. The mutants had alpha-subunits truncated before position Lys28 (alpha delta K28) or Thr29 (alpha delta T29) of the N-terminus. The currents generated by all variants of pump molecules in the presence of 5 mM K+ show voltage-dependent inhibition by external [Na+]. The apparent KI values increase with membrane depolarisation, and the potential dependence can be described by the movement of effective charges in the electrical potential gradient across the membrane. Taking into account Na(+)-K+ competition for external binding to the E2P form, apparent KI values and effective charges for the interaction of the Na+ ions with the E2P form can be estimated. For the Xenopus pump the effective charge amounts to 1.1 of an elementary charge and the KI value at 0 mV to 44 mM. For the wild-type Torpedo pump, the analysis yields values of 0.73 of an elementary charge and 133 mM, respectively. Truncation at the N-terminus removing a lysine-rich cluster of the alpha-subunit of the Torpedo pump leads to an increase of the effective charge and decrease of the KI value. For alpha delta K28, values of 0.83 of an elementary charge and 117 mM are obtained, respectively. If Lys28 is included in the truncation (alpha delta T29), the effective charge increases to 1.5 of an elementary charge and the apparent KI value is reduced to 107 mM. The KI values for pump inhibition by external Na+, calculated by taking into account Na(+)-K+ competition, are smaller than the K1/2 values determined in the presence of 5 mM [K+]. The difference is more pronounced for those pump variants that have higher Km values. The variations of the parameters describing inhibition by external [Na+] are qualitatively similar to those described for the stimulation of the pumps by external [K+] in the absence of extracellular [Na+]. The observations may be explained by an access channel within the membrane dielectric that has to be passed by the external Na+ and K+ ions to reach or leave their binding sites. The potential-dependent access and/or the interaction with the binding sites shows species differences and is affected by cytoplasmic lysine residues in the N-terminus.

Animals↗
PubMed1993

The expression of bovine microsomal cytochrome b5 in Escherichia coli and a study of the solution structure and stability of variant proteins.

The DNA sequence of bovine microsomal cytochrome b5 has been amplified from a liver cDNA library using a polymerase chain reaction. The amplified cDNA when cloned into plasmids that support the high-level production of cytochrome b5 in E.coli leads to protein overexpression and results in cell colonies bearing a strong red colouration. Using cassette mutagenesis, truncated versions of the cytochrome b5 cDNA have been made that encode the first 90 amino acid residues (Ala1-Lys90), the first 104 amino acids (Ala1-Ser104) and the complete protein (Ala1-Asn133). The location of the overexpressed cytochrome b5 within prokaryotic cells is dependent on the overall length of the protein. Expression of the Ala-Lys90 and Ala1-Ser104 variants leads to a location in the cytoplasmic phase of the bacteria whereas the whole protein, Ala1-Asn133, is found within the bacterial membrane fraction. The last 30 residues of cytochrome b5 therefore contain all of the necessary information to insert the protein into E.coli membranes. The solubility of the Ala1-Ser104 variant permits the solution structure and stability of this protein to be measured using 1- and 2-D 1H-NMR methods and electronic spectroscopy. 1-D NMR studies show that the chemical shifts of the haem and haem ligand resonances of the Ala1-Ser104 variant exhibit only very slight perturbations to their magnetic microenvironments when compared with the tryptic fragment of ferricytochrome b5. These results indicate an arrangement of residues in the haem pocket that is very similar in both the Ala1-Ser104 variant and the tryptic fragment and by 2-D NMR it is shown that this similarity extends to the conformations of the polypeptide backbone and side chains. Electronic spectroscopy of this variant shows absorbance maxima for the Soret peaks at 423 nm (reduced) and 413 nm (oxidized). From absorbance spectra the relative thermal stabilities of the Ala1-Ser104 variant and the tryptic fragment were measured. In the oxidized state the Ala1-Ser104 variant denatures in a single cooperative transition with a midpoint temperature (Tm) of 73 degrees C that is significantly higher than that of 'tryptic' ferricytochrome b5. The reduced form of the protein shows increased transition temperatures (Tm approximately 78 degrees C) reflected in the values of delta Hm, delta Sm and delta(delta G) of 420 kJ/mol, 1096 J/mol/K and 12.38 kJ/mol respectively, estimated for this variant. The increased stability of the Ala1-Ser104 variant and other recombinant forms of cytochrome b5 is correlated with the presence of additional residues at the N- and C-termini.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Cellular responses to Plasmodium falciparum erythrocyte membrane protein-1: use of relatively conserved synthetic peptide pools to determine CD4 T cell responses in malaria-exposed individuals in Benin, West Africa.

BACKGROUND: Plasmodium falciparum erythrocyte membrane protein-1, a variant antigen of the malaria parasite, is potentially a target for the immune response. It would be important to determine whether there are CD4 T cells that recognise conserved regions. However, within the relatively conserved region, there is variation. It is not possible to test T cell responses from small field samples with all possible peptides. METHODS: We have aligned sequences that are relatively conserved between several PfEMP1 molecules, and chosen a representative sequence similar to most of the PfEMP1 variants. Using these peptides as pools representing CIDRalpha, CIDRbeta and DBLbeta-delta domains, DBLalpha domain, and EXON 2 domain of PfEMP1, we measured the CD4 T cell responses of malaria-exposed donors from Benin, West Africa by a FACS based assay. RESULTS: All the three peptide pools elicited a CD4 T cell response in a proportion of malaria-exposed and non-exposed donors. CD4 T cell proliferation occurs at a relatively higher magnitude to peptide pools from the DBLalpha and EXON 2 in the malaria-exposed donors living in Benin than in the UK malaria-unexposed donors. CONCLUSIONS: These findings suggest that an immunological recall response to conserved peptides of a variant antigen can be measured. Further testing of individual peptides in a positive pool will allow us to determine those conserved sequences recognised by many individuals. These types of assays may provide information on conserved peptides of PfEMP1 which could be useful for stimulating T cells to provide help to P. falciparum specific B cells.

Adolescent↗
PubMed2006

Hepatitis delta virus super-infection in a co-infected patient with the human immunodeficiency virus type 1 and a surface antigen-negative hepatitis B virus variant.

Human immunodeficiency virus infection has a major impact on the natural history of chronic hepatitis B and favours the emergence of viral mutants. We describe an acute hepatitis D virus superinfection in an HIV-1-infected patient under HAART treatment who was previously a chronic carrier of a surface negative HBV variant resistant to lamivudine.

Adenine↗
PubMed1991

Replacement of finger and growth factor domains of tissue plasminogen activator with plasminogen kringle 1. Biochemical and pharmacological characterization of a novel chimera containing a high affinity fibrin-binding domain linked to a heterologous protein.

A novel triple-kringle plasminogen activator protein, PK1 delta FE1X, has been produced which is a genetic chimera between the fibrin binding kringle 1 domain of plasminogen and the two kringles and serine protease domains of naturally occurring wild-type tissue plasminogen activator (wt t-PA). This chimera also contains a modification to prevent high mannose type N-linked glycosylation on kringle 1 of t-PA. PK1 delta FE1X is biochemically and fibrinolytically similar to wt t-PA in vitro but retains the decreased plasma clearance rate characteristic of other t-PA variants which lack fibronectin finger-like and epidermal growth factor domains. The serine protease domain of PK1 delta FE1X exhibits the amidolytic activity characteristic of wt t-PA. In an indirect coupled plasminogen activator assay, the specific activity of PK1 delta FE1X is approximately 1.4 times greater than that of wt t-PA. In a fibrin film-binding assay, greater binding to untreated fibrin is observed with wt t-PA than with PK1 delta FE1X. However, following limited plasmin digestion of the fibrin film, PK1 delta FE1X binding increases to the level observed with wt t-PA. The incremental binding to plasmin-digested fibrin observed with PK1 delta FE1X is eliminated if plasmin digestion of the fibrin film is followed by carboxypeptidase B treatment. This result suggests that plasminogen kringle 1 binds plasmin-digested fibrin even after recombination with a heterologous protein. The fibrinolytic activity of PK1 delta FE1X in human plasma clot lysis assays was similar to that of wt t-PA at activator concentrations of approximately 1 microgram/ml. At substantially lower concentrations, approximately 0.1 microgram/ml, PK1 delta FE1X was only slightly less active than wt t-PA. Pharmacokinetic analysis showed that wt t-PA activity is cleared approximately 15 times as rapidly as PK1 delta FE1X following intravenous bolus injection. In a rabbit jugular vein clot lysis model, intravenous bolus injection of 0.06 mg/kg of PK1 delta FE1X showed greater thrombolytic potency than a similar administration of 0.5 mg/kg of wt t-PA. Thus it appears that in vitro exon shuffling techniques can be used to generate novel fibrinolytic agents which biochemically and pharmacologically represent the combination of individual domains of naturally occurring proteins.

Amino Acid Sequence↗
PubMed1995

The hinge region of Escherichia coli ribosomal protein L7/L12 is required for factor binding and GTP hydrolysis.

A variant form of Escherichia coli ribosomal protein L7/L12 that lacked residues 42 to 52 (L7/L12: delta 42-52) in the hinge region was shown previously to be completely inactive in supporting polyphenylalanine synthesis although it bound to L7/L12 deficient core particles with the normal stoichiometry of four copies per particle (Oleinikov AV, Perroud B, Wang B, Traut RR (1993) J Biol Chem, 268, 917-922). The result suggested that the hinge confers flexibility that is required for activity because the resulting bent conformation allows the distal C-terminal domain to occupy a location on the body of the large ribosomal subunit proximal to the base of the L7/L12 stalk where elongation factors bind. Factor binding to the hinge-truncated variant was tested. As an alternative strategy to deleting residues from the hinge, seven amino acid residues within the putative hinge region were replaced by seven consecutive proline residues in an attempt to confer increased rigidity that might reduce or eliminate the bending of the molecule inferred to be functionally important. This variant, L7/L12:(Pro)7, remained fully active in protein synthesis. Whereas the binding of both factors in ribosomes containing L7/L12:delta 42-52 was decreased by about 50%, there was no loss of factor binding in ribosomes containing L7/L12:(Pro)7, as predicted from the retention of protein synthesis activity. The factor:ribosome complexes that contained L7/L12:delta 42-52 had the same low level of GTP hydrolysis as the core particles completely lacking L7/L12 and EF-G did not support translocation measured by the reaction of phe-tRNA bound in the A site with puromycin. It is concluded that the hinge region is required for the functionally productive binding of elongation factors, and the defect in protein synthesis reported previously is due to this defect. The variant produced by the introduction of the putative rigid Pro7 sequence retains sufficient flexibility for full activity.

Amino Acid Sequence↗
PubMed1990

RNA primary sequence or secondary structure in the translational initiation region controls expression of two variant interferon-beta genes in Escherichia coli.

Efficient expression in Escherichia coli (E. coli) of the human interferon-beta gene (IFN-beta) gene and of a chemically synthesized IFN-beta gene variant (506 base pairs; synIFN-beta) adapted to the E. coli codon usage, both fused to the E. coli atpE ribosome-binding site, is controlled either by primary sequence or by mRNA secondary-structure in the translational initiation region. High level expression of the natural human atpE/IFN-beta gene fusion is governed by the nucleotide composition preceding the initiator codon AUG. A single U----C exchange in the -2 or -1 position preceding the initiator codon AUG reduces the translational efficiency from 18% of total cellular protein to only 8% or 4%, respectively, while both U----C substitutions reduce IFN-beta expression below 1%. These sequence alterations interfere with efficient ribosome binding as revealed by toeprinting. They provide further evidence for the influence of the anticodon-flanking regions of tRNA(fMet) upon the initiation rate of translation. In contrast, translation of the synthetic variant atpE/synIFN-beta gene fusion is controlled by a moderately stable stem-loop structure (delta G = -4 kcal/mol; 37 degrees C) located within the coding region and overlapping the 30 S ribosomal subunit attachment site. That the stability of the hairpin interferes with the initiation of translation is inferred from site-directed mutagenesis and toeprint analyses. mRNA half-life in these variants is positively correlated with the rate of translation and involves two major endonucleolytic cleavage site 5'-upstream of the Shine-Dalgarno region.

Base Sequence↗
PubMed1991

Structural and catalytic properties of a deletion derivative (delta 133-157) of Escherichia coli adenylate kinase.

Escherichia coli adenylate kinase (AKe) as well as the enzyme from yeast and mitochondria differs from the muscle cytosolic variant (AK1) by an insertion of 25 amino acid residues that are missing in AK1. The extra sequence, highly homologous in "large" size variants, is situated between residues 133 and 157 in AKe. Removal of 25 codons in the corresponding adk gene resulted in expression of a modified form of adenylate kinase (delta 133-157 AKe) which still conserved 7% of the maximal activity of the wild-type protein. The apparent Km for nucleotide substrates was increased by a factor of 4.6 (ADP), 23 (ATP) or 43 (AMP) in delta 133-157 AKe when compared with the wild-type enzyme. The secondary structure of delta 133-157 AKe, as well as its thermal stability were very similar to the parent protein. However, the deleted protein was much more sensitive than the wild-type enzyme to inactivation by trypsin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of trypsin digested delta 133-157 AKe revealed accumulation of several well defined fragments which were not observed in the case of wild-type enzyme. We conclude that the additional sequence, although necessary for expression of full activity in AKe, is not critical for catalysis. It is perhaps responsible for interaction of enzyme with other cellular components although a different mechanism of water shielding for large and small size variants of AK can be also envisaged.

Adenylate Kinase↗
PubMed1998

Transcriptional regulation and induction of apoptosis: implications for the use of monomeric p53 variants in gene therapy.

The p53 tumour suppressor protein is a transcriptional activator, which can induce cell cycle arrest and apoptosis. p53 Gene mutations occur in more than 50% of all human tumours. Reintroduction of wild-type p53 but also of oligomerisation-independent p53 variants into tumour cells by gene transfer methods has been considered. We have investigated the biological properties of two carboxy-terminal deletion mutants of p53, p53 delta 300 (comprising amino acids 1-300) and p53 delta 326 (amino acids 1-326), to evaluate their potential deployment in gene therapy. Transactivation was measured in transiently transfected HeLa and SKBR3 cells. Both monomeric variants showed reduced activities compared with wild-type p53. Individual promoters were differently affected. In contrast to wild-type p53, monomeric variants were not able to induce apoptosis. We also provided wild-type p53 and p53 delta 326 with tetracycline-regulated promoters and stably introduced these constructs into Saos2 and SKBR3 cells. Upon induction, wild-type p53 expressing cells, but not p53 delta 326 expressing cells underwent apoptosis. Consistently, only wild-type p53 expressing cells accumulated p21/waf1/cip1 mRNA and protein and showed increased bax, Gadd45 and mdm2 mRNA. Neither wild-type p53 nor p53 delta 326 repressed the transcription of the IGF-1R gene in these cell lines. We conclude that the transactivation potential of monomeric, carboxy-terminally truncated p53 is not sufficient to cause induction of the endogenous target genes which trigger apoptosis.

Apoptosis↗