MCA/MR syndrome in two female siblings: new entity or variant examples of Coffin-Lowry versus Atkin-Flaitz syndromes?

We report two sisters with mental retardation, coarse facial features, telecanthus, flat malar region, prominent lower lip, kyphoscoliosis, and tapering fingers. Although these patients' phenotypes showed considerable overlap with the Coffin-Lowry and the Atkin-Flaitz syndromes, their overall picture makes these diagnoses controversial.     

Regulation of intracellular pH in LLC-PK1 cells studied using 31P-NMR spectroscopy

31P-NMR spectroscopy was used to monitor intracellular pH (pHi) in a suspension of LLC-PK1 cells, a renal epithelial cell line. The regulation of intracellular pH (pHi) was studied during intracellular acidification with 20% CO2 or intracellular alkalinization with 30 mM NH4Cl. The steady-state pHi in bicarbonate-containing Ringer's solution (pHo 7.40) was 7.14 +/- 0.04 and in bicarbonate-free Ringer's solution (pHo 7.40) 7.24 +/- 0.04. When pHo was altered in nominally HCO3(-)-free Ringer's, the intracellular pHi changed to only a small extent between pHo 6.6 and pHo 7.6; beyond this range pHi was linearly related to pHo. Below pHo 6.6 the cell was capable of maintaining a delta pH of 0.2 pH unit (inside more alkaline), above pH 7.6 a delta pH of 0.4 unit could be generated (inside more acid). During exposure to 20% CO2 in HCO3(-)-free Ringer's solution, pHi dropped initially to 6.9 +/- 0.05, the rate of realkalinisation was found to be 0.071 pH unit X min-1. After removal of CO2 the pHi increased by 0.65 and the rate of reacidification was 0.056 pH unit X min-1. Exposure to 30 mM NH4Cl caused a raise of pHi by 0.48 pH unit and an initial rate of re-acidification of 0.063 pH unit X min-1, after removal of NH4Cl the pHi fell by 0.58 pH unit below the steady-state pHi, followed by a subsequent re-alkalinization of 0.083 pH unit X min-1. Under both experimental conditions, the pHi recovery after an intracellular acidification, introduced by exposure to 20% CO2 and by removal of NH4+, was found to be inhibited by 53% and 63%, respectively, in the absence of sodium and 60% and 72%, respectively, by 1 mM amiloride. These studies indicate that 31P-NMR can be used to monitor steady-state intracellular pH as well a pHi transients in suspensions of epithelial cells. The results support the view that LLC-PK1 cells use an Na+-H+ exchange system to readjust their internal pH after acid loading of the cell.     

13C-n.m.r. study of citrate metabolism in rabbit renal proximal-tubule cells.

U.v.-visible-absorption and e.p.r. spectroscopy were used to study the type 2 and type 3 copper centres in the mercury derivative of laccase. After treatment with peroxide the mercury derivative of laccase exhibits a fully developed absorption band at 330 nm (delta epsilon = 2900 +/- 100 M-1.cm-1, which is characteristic of type 3 copper in the oxidized state. In addition, there is a weak ligand-field absorption at 740 nm (epsilon = 380 +/- 30 M-1.cm-1), which can be assigned to the type 3 pair. Because the e.p.r. spectrum of the type 2 copper is well resolved in the case of the mercury derivative of laccase, for the first time we have been able to observe spectroscopic evidence for a pH-dependent structural transition that has been invoked to explain the kinetics of enzyme reduction [Andréasson & Reinhammar (1979) Biochim. Biophys. Acta 568, 145-156]. According to the e.p.r. data the pKa lies in the range 6-7, and comparisons with a model compound show that the spectral changes can plausibly be interpreted in terms of the deprotonation of a water molecule in the co-ordination sphere of the type 2 copper.     

Kinetic parameters of the protein tyrosine kinase activity of EGF-receptor mutants with individually altered autophosphorylation sites.

Epidermal growth factor (EGF)-receptor mutants in which individual autophosphorylation sites (Tyr1068, Tyr1148 or Tyr1173) have been replaced by phenylalanine residues were expressed in NIH-3T3 cells lacking endogenous EGF-receptors. Kinetic parameters of the kinase of wild-type and mutant receptors were compared. Both wild-type and mutant EGF-receptors had a Km(ATP) 1-3 microM for the autophosphorylation reaction, and a Km(ATP) of 3-7 microM for the phosphorylation of a peptide substrate. These are similar to the Km(ATP) values reported for EGF-receptor of A431 cells. A synthetic peptide representing the major in vitro autophosphorylation site Tyr1173 of the EGF-receptor (KGSTAENAEYLRV) was phosphorylated by wild-type receptor with a Km of 110-130 microM, and the peptide inhibited autophosphorylation with a Ki of 150 microM. Mutant EGF-receptors phosphorylated the peptide substrate with a Km of 70-100 microM. A similar decrease of Km (substrate) was obtained when the phosphorylation experiments were performed with the commonly applied substrates angiotensin II and a peptide derived from c-src. The Km of angiotensin II phosphorylation was reduced from 1100 microM for wild-type receptor to 890 microM for mutant receptor and for c-src peptide from 1010 microM to 770 microM respectively. The Vmax of the kinase was dependent on receptor concentration, but was not significantly affected by the mutation. Analogs of the Tyr1173 peptide in which the tyrosine residue was replaced by either a phenylalanine or an alanine residue also inhibited autophosphorylation with Ki of 650-750 microM. These analyses show that alterations of individual autophosphorylation sites do not have a major effect on kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

The root-knot nematode resistance gene (Mi) in tomato: construction of a molecular linkage map and identification of dominant cDNA markers in resistant genotypes

A dominant allele at the Mi locus on chromosome 6 of tomato (Lycopersicon esculentum Mill) confers resistance to three species of root-knot nematodes (Meloidogyne). The resistance, which is associated with a localized necrotic response, was originally introduced into tomato from the wild species Lycopersicon peruvianum. As a step towards the molecular cloning of Mi, we have identified closely linked DNA markers from both cDNA and genomic DNA libraries as restriction fragment length polymorphisms (RFLPs). DNA from tomato populations segregating for nematode resistance was analyzed to generate a high-resolution genetic map of this region. Additional information on gene order was obtained by comparing the size of the introgressed L. peruvianum chromosomal segment within a collection of nematode-resistant tomato lines. Among the four cDNA markers that are tightly linked to Mi, three are dominant, i.e. L. peruvianum-specific. One cDNA marker corresponds to a gene family comprising 20-30 members, one of which is diagnostic for all nematode-resistant genotypes tested. The presence of non-homologous sequences around the Mi gene may contribute to the suppression of recombination in this region of the genome in crosses heterozygous for Mi. The potential of 'walking' from closely linked markers to Mi is discussed.     

The rate of nuclear cytoplasmic protein transport is determined by the casein kinase II site flanking the nuclear localization sequence of the SV40 T-antigen.

We have previously demonstrated [Rihs, H.-P. and Peters, R. (1989) EMBO J., 8, 1479-1484] that the nuclear transport of recombinant proteins in which short fragments of the SV40 T-antigen are fused to the amino terminus of Escherichia coli beta-galactosidase is dependent on both the nuclear localization sequence (NLS, T-antigen residues 126-132) and a phosphorylation-site-containing sequence (T-antigen residues 111-125). While the NLS determines the specificity, the rate of transport is controlled by the phosphorylation-site-containing sequence. The present study furthers this observation and examines the role of the various phosphorylation sites. Purified, fluorescently labeled recombinant proteins were injected into the cytoplasm of Vero or hepatoma (HTC) cells and the kinetics of nuclear transport measured by laser microfluorimetry. By replacing serine and threonine residues known to be phosphorylated in vivo, we identified the casein kinase II (CK-II) site S111/S112 to be the determining factor in the enhancement of the transport. Either of the residues 111 or 112 was sufficient to elicit the maximum transport enhancement. The other phosphorylation sites (S120, S123, T124) had no influence on the transport rate. Examination of the literature suggested that many proteins harboring a nuclear localization sequence also contain putative CK-II sites at a distance of approximately 10-30 amino acid residues from the NLS. CK-II has been previously implicated in the transmission of growth signals to the nucleus. Our results suggest that CK-II may exert this role by controlling the rate of nuclear protein transport.     

Pathways for organic osmolyte synthesis in rabbit renal papillary tissue, a metabolic study using 13C-labeled substrates

Renal papillary collecting duct cells have been postulated to adapt their intracellular osmolality to the large changes in interstitial osmolality by changing their content of 'non-perturbing' organic osmolytes such as sorbitol and myo-inositol. 13C-NMR was used in this study to elucidate the metabolic pathways leading to a synthesis of those compounds. Incubation of rabbit renal papillary tissue with [1-13C]glucose showed label scrambling mainly into sorbitol (C-1) and lactate (C-3). This result confirms activity of aldose reductase and glycolytic enzymes in renal papillary cells. Using [3-13C]alanine or [2-13C]pyruvate as carbon source, 13C-labeling of sorbitol and myo-inositol was observed, indicating that renal papillary tissue possesses, in addition, gluconeogenic activity. The latter assumption is supported by the result that in enzyme assays rabbit kidney papilla and isolated rat kidney papillary collecting duct cells show significant fructose-1,6-bisphosphatase activity.     

Expression cloning of a cDNA encoding the type II regulatory subunit of the cAMP-dependent protein kinase

We report here the isolation and sequence of a cDNA for the type II regulatory subunit of the cAMP-dependent protein kinase (cAMP-PK) from a lambda gt-11 cDNA library derived from a porcine epithelial cell line (LLC-PK1). The cDNA was detected by immunological screening using an affinity purified polyclonal antibody for bovine RII. DNA sequence analysis of the 467 bp EcoRI insert confirmed the identity of the clone, because the deduced amino acid sequence corresponded to the published sequence for the bovine RII protein. Northern analysis of total RNA from the LLC-PK1 cells indicated a single mRNA species of about 6.0 kb, probably derived from a single copy gene.     

Complementation between uncF alleles affecting assembly of the F1F0-ATPase complex of Escherichia coli.

A mutant affected in the b subunit (coded by the uncF gene) of the F1F0-ATPase in Escherichia coli was isolated by a localized mutagenesis procedure in which a plasmid carrying the unc genes was mutagenized in vivo. The biochemical properties of cells carrying the uncF515 allele were examined in a strain carrying the allele on a multicopy plasmid and a mutator-induced polar unc mutation on the chromosome. The strain carrying the mutant unc allele was uncoupled with respect to oxidative phosphorylation. Membrane-bound ATPase activity was very low or absent, and membranes were somewhat proton permeable. It was concluded that the F0 sector was assembled. Determination of the DNA sequence of the uncF515 allele showed it differed from wild type in that a G----A substitution occurred at position 392, resulting in glycine being replaced by aspartate at position 131. Genetic complementation tests indicated that the uncF515 allele complemented the uncF476 allele (Gly 9----Asp). Two-dimensional gel electrophoresis of membrane preparations indicated that the uncF515 and uncF476 alleles interrupted assembly of the F1F0-ATPase at different stages.