3-Oxoacyl-[ACP] reductase from oilseed rape (Brassica napus).

3-Oxoacyl-[ACP] reductase (E.C. 1.1.1.100, alternatively known as beta-ketoacyl-[ACP] reductase), a component of fatty acid synthetase has been purified from seeds of rape by ammonium sulphate fractionation, Procion Red H-E3B chromatography, FPLC gel filtration and high performance hydroxyapatite chromatography. The purified enzyme appears on SDS-PAGE as a number of 20-30 kDa components and has a strong tendency to exist in a dimeric form, particularly when dithiothreitol is not present to reduce disulphide bonds. Cleveland mapping and cross-reactivity with antiserum raised against avocado 3-oxoacyl-[ACP] reductase both indicate that the multiple components have similar primary structures. On gel filtration the enzyme appears to have a molecular mass of 120 kDa suggesting that the native structure is tetrameric. The enzyme has a strong preference for the acetoacetyl ester of acyl carrier protein (Km = 3 microM) over the corresponding esters of the model substrates N-acetyl cysteamine (Km = 35 mM) and CoA (Km = 261 microM). It is inactivated by dilution but this can be partly prevented by the inclusion of NADPH. Using an antiserum prepared against avocado 3-oxoacyl-[ACP] reductase, the enzyme has been visualised inside the plastids of rape embryo and leaf tissues by immunoelectron microscopy. Amino acid sequencing of two peptides prepared by digestion of the purified enzyme with trypsin showed strong similarities with 3-oxoacyl-[ACP] reductase from avocado pear and the Nod G gene product from Rhizobium meliloti.     

Response of macroinvertebrates to blooms of iron-depositing bacteria

In field measurements and laboratory experiments we assessed the influence of high levels of iron, manganese, and concurrent blooms of iron-depositing bacteria, Leptothrix ochracea, on macroinvertebrates. Macroinvertebrate communities in five of six streams were depauerate inside blooms. Reasons for the decreased abundance vary among taxa, with our experiments demonstrating the importance, for one or more species, of (1) direct toxic effects, and,/or smothering, (2) behavioral avoidance of bacterial-coated substrates, and (3) an inability to use bacteria as food. Three mayfly species showed increased mortality when caged inside the blooms, but five trichopterans and one plecopteran did not. Five invertebrates avoided Leptothrix-coated substrate in choice trials, while three did not. Stenonema fuscum could not ingest Leptothrix, and Neophylax nacatus had reduced growth feeding on it, but Heptagenia umbratica grew equally well on diets of Leptothrix or diatoms. This study demonstrates the important role epilithic organisms play in modifying substrates, and how these changes may act to influence benthic abundance and distribution in streams.     

Cystinotic and normal fibroblasts: Differential susceptibility to cysteine toxicity in vitro

Summary Extracellular cysteine concentrations between 0.5 and 2.5 mM resulted in death of normal but not cystinotic cells grown in Eagle's minimal essential medium containing supplemental fetal bovine serum and antibiotics. Differential cell survival was determined by viable cell counting using Trypan Blue dye exclusion. In cocultivation experiments of [³H]thymidine-labelled cystinotic fibroblasts with nonradioactive normal fibroblasts, autoradiography confirmed the selective survival of cystinotic cells in medium containing 1 mM cysteine. At this concentration of 1 mM cysteine, intracellular cystine content increased slightly in surviving normal cells but not in cystinotic cells, which normally contain a high level of intracellular cystine. This comparative resistance of cystinotic fibroblasts to elevated extracellular cysteine concentrations forms the basis for an in vitro selective system for these mutant human cells. Further exploration of this resistance phenomenon may well expand the understanding of the molecular defect in cystinotic cells.     

Rabbit heavy chain haplotypes — Allotypic determinants expressed byVH-CH recombinants

This report summarizes our current understanding of the heavy chain haplotypes found in our laboratories' rabbits. Independently derived data from several laboratories have been synthesized into a consistent picture of the linked inheritance of allotypic markers found on the different heavy chain classes and subclasses of rabbit immunoglobulins in pedigreed rabbits, including the families of three apparentVH-CH recombinants. In one recombinant, the entire group ofCH markers (C, C, and C) recombined with the set ofVH. Although in the other two recombinants all CH markers may also have recombined as a group, in one of these only IgG and IgACH genes were informative; in the other recombinant, only the IgG allotypes were informative. Some allotypic determinants found on IgM molecules (conformational) appear only when a specific variable region allotype (VHa) is combined with a specific constant region allotype (C). New combinations ofVHa and C allotypes were generated in two of the genetic recombinants and led to new conformational determinants. The gains and losses observed lend support to the hypothesis that the determinants result from conformations generated by the combination of allotype-specificVH and C protein sequences. Conceivably, DNA events that joinVH to diversity (D)- and joining (J)-coding sequences or mRNA processing events that splice J to C could be involved in generating the sequences that form allotype-specific determinants.     

Some perspectives on the transfer of cell-mediated immunity by immune-RNA

Summary Ribonucleic acid extracts of lymphoid cells from immune hosts were used to transfer in vivo and in vitro cell-mediated immune reactivity to a variety of antigens. The in vivo immune responses transferred by RNA included the delayed cutaneous hypersensitivity reaction to fungal and chemically-defined antigens and the tumor-rejection reaction to guinea pig hepatoma antigens. The in vitro immune responses transferred by RNA included macrophage migration inhibition by fungal, chemically-defined, and tumor antigens. The transfer activity of RNA preparations was contained in the 8 s to 18 s species of RNA and was sensitive to RNAse but not to DNase or trypsin. Antigen was not detectable in the RNA preparations and appeared to have no role in the transfer activity. Syngeneic, allogeneic, or xenogeneic sources of RNA could transfer immune reactivity. In each system tested, the transfer of cell-mediated reactivity by RNA was specific for the antigen used to sensitize the RNA donor. The potential use of RNA-mediated transfer of immunity is discussed.     

Infiltration of central nervous system in adult acute myeloid leukaemia.

Out of 64 consecutive unselected patients with acute myeloid leukaemia studied during 1973-6, five developed clinical evidence of spread to the central nervous system (CNS). Neuroradiological examination showed cerebral deposits in three, in whom rapid symptomatic relief was obtained with radiotherapy. In two of these patients who developed solid intracranial deposits haematological remission could be reinduced or maintained; they were still alive 86 and 134 weeks later. When patients presented with spread to the CNS complicating generalised uncontrolled leukaemia they had short survivals. CNS infiltration may respond dramatically to appropriate treatment provided that it is not associated with generalised uncontrolled leukaemia, which has a poor prognosis. In view of this, routine "prophylaxis" of the CNS in adult acute myeloid leukaemia does not seem justified at present.     

Context Effects on Nonsense Codon Suppression in ESCHERICHIA COLI

The influence of mRNA context on nonsense codon suppression has been studied by suppression measurements at one site in the Escherichia coli trpE gene and at two sites in the trpA gene. The ratio of suppression efficiencies of amber and ochre codons at each site (homotopic pairs) has been compared using ochre suppressing derivatives of tRNATyr. This ratio is independent of differential effects of the inserted amino acid on enzyme function. We have found that mRNA context can change the ratio of suppression efficiencies of homotopic nonsense codons at the three sites in the trp gene system over a ten-fold range. The causes of such variation, and, in particular the effect of certain adjacent nucleotides on nonsense codon suppression are considered.     

Expression of Escherichia coli fol alleles in Salmonella typhimurium.

Studies of the expression of Escherichia coli fol alleles in Salmonella typhimurium indicated that fol regulatory functions are highly conserved between these bacterial species.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.