The detergent solubility properties of a malarial (Plasmodium knowlesi) variant antigen expressed on the surface of infected erythrocytes

Four detergents have been compared for identification of the Plasmodium knowlesi variant antigen on infected erythrocytes by immunoprecipitation analysis. Erythrocytes infected with late trophozoite and schizont forms of cloned asexual parasites were labeled by lactoperoxidase-catalyzed radioiodination and extracted either with the anionic detergents sodium dodecyl sulfate (SDS) or cholate, the neutral detergent Triton X-100, or the zwitterion 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS). After addition of Triton X-100 to SDS and cholate extracts, parallel immunoprecipitations of the four extracts were performed using rhesus monkey antisera of defined agglutinability. Identical results were obtained with clone Pk1(A+), which has 125I-variant antigens of Mr 210,000 and 190,000, and with clone Pk1(B+)1+, which has variant antigens of Mr 200,000-205,000. SDS yielded maximal levels of immunoprecipitated 125I-variant antigens. Variant-specific immunoprecipitation was detected in some experiments with Triton X-100 and cholic acid but with significantly lower recovery than with SDS. CHAPS extraction did not yield the variant antigens on immunoprecipitation. The variant antigens could also be identified in Triton X-100-insoluble material by subsequent extraction with SDS, indicating that failure to recover these proteins in the Triton X-100-soluble fraction is due to failure of this detergent to extract the variant antigens rather than to degradation during extraction. We suggest that the 125I-variant antigens either have a structure that renders them intrinsically insoluble in Triton X-100, cholate, or CHAPS, or that they are associated in some way with host cell membrane components that also resist solubilization by these detergents.     

Low molecular weight nuclear RNA in human lymphocytes : A comparison of PHA-treated and control cells

Seven species of low molecular weight nuclear (LMN) RNA were identified in human peripheral lymphocytes. These were designated as A, B, C, D, D′, E and F. The same 7 species of LMN RNA were obtained from resting lymphocytes and from lymphocytes exposed to PHA for 16 and 60 h, respectively. Thus, no detectable qualitative changes were seen in the spectrum of LMN RNAs during PHA-induced lymphocyte transformation. However, the amount of species A, D-D′, E and F per nucleus in fully transformed cells was greater than in untreated lymphocytes. This increase had not yet occurred after 16 h treatment with PHA. ³H-Uridine was incorporated into all species of LMN RNA of resting and PHA-treated lymphocytes. Furthermore, all species of LMN RNA except C (5S RNA) were methylated in both resting and transformed cells. The ³H and ¹⁴C specific activities of LMN RNAs following an 8 h exposure to ³H-uridine and ¹⁴C-methyl methionine were higher in PHA-treated cells than in untreated lymphocytes. For several species of LMN RNA (A, D-D′, E, F) the highest ³H and ¹⁴C spec. act. were observed after 16 h exposure to PHA. The possibility that quantitative alterations in the synthesis and methylation of LMN RNAs may occur during lymphocyte transformation is discussed.     

Changes in DNA and RNA synthesis and associated enzyme activities after the stimulation of serum-depleted BHK21-C13 cells by the addition of serum

BHK21/C13 cells placed in medium containing low (1%) serum ceased DNA synthesis within 4 days. DNA synthesis recommenced 10 h after the readdition of serum (to 10%) to cells incubated for 6 days in serum-depleted medium. Two peaks of thymidine incorporation were observed at 12–13 h and 15–17 h, followed by a single peak of dividing cells at 25 h. The two peaks of incorporation represent variation in the extent of DNA replication during a single synchronous S phase.Uridine, deoxyadenosine and deoxyguanosine kinase activities did not decline in serum-depleted cells and, after the addition of serum, their activities showed cyclical variation about a mean involving two-fold changes in enzyme specific activity. All other enzyme activities examined were markedly decreased in resting cells.Ornithine decarboxylase activity increased 15-fold within 5 h of serum addition, but had returned to the resting level by 8 h. There was no apparent correlation between this alteration of enzyme activity and the rate of RNA synthesis.DNA polymerase, thymidine kinase and deoxycytidine kinase activities all decreased further within 4 h of the addition of serum, followed by several-fold increases in activity. The peak of DNA polymerase activity corresponded to, and encompassed, both peaks of DNA synthesis. However, thymidine and deoxycytidine kinase activities, although exhibiting two activity maxima corresponding to the peaks of DNA synthesis, were at their highest levels in G2.     

Inhibition of dopamine uptake by N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a cause of parkinsonism

N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine has been reported to cause parkinsonism in man and monkeys, producing behavioral effects within 5 min of administration. The compound reversibly and competively inhibited (IC50 = 2 microM) dopamine uptake into PC12, a clonal line of rat pheochromocytoma cells that store and secrete dopamine and acetylcholine. Uptake of choline and 2-deoxyglucose was not affected. Prolonged exposure to the compound was lethal to PC12; survivors of this treatment lost the ability to store dopamine and acetylcholine and to extend neurites upon incubation with nerve growth factor.     

Contraceptives,counselling, and pregnancy in women with sickle cell disease.

Sickle cell disease is listed in the manufacturers'' data sheets in the United Kingdom as a contraindication to the use of most combined contraceptive pills; the result is confused advice on family planning to a group of women who are at substantial risk from both planned and unplanned pregnancy. A study in north London on the use of contraceptives by women with sickle cell disease indicates that the use of combined oral contraceptives is common. Although medical staff usually advised against pregnancy, such advice was almost always ignored. Over half of the women surveyed had some knowledge about antenatal diagnosis. Family planning advice should be an integral part of the care of women with sickle cell disease. In the absence of specific data to the contrary all methods of contraception may be considered, although with appropriate caution.     

A single genetic locus in the phytopathogen Pantoea stewartii enables gut colonization and pathogenicity in an insect host

Aphids are typically exposed to a variety of epiphytic and phytopathogenic bacteria, many of which have entomopathogenic potential. Here we describe the interaction between Pantoea stewartii ssp. stewartii DC283 (DC283), an enteric phytopathogen and causal agent of Stewart's wilt, and the pea aphid, Acyrthosiphon pisum . When ingested by aphids, DC283 establishes and aggregates in the crop and gut, preventing honeydew flow and excretion, resulting in aphid death in 72 h. A mutagenesis screen identified a single locus, termed ucp1 (yo u c annot p ass), whose disruption abolishes aphid pathogenicity. Moreover, the expression of ucp1 in Escherichia coli is sufficient to mediate the hindgut aggregation phenotype by this normally avirulent species. Ucp1 is related to six other proteins in the DC283 genome, each having a common N-terminal region and a divergent C-terminus, but only ucp1 has a role in pathogenicity. Based on predicted motifs and secondary structure, Ucp1 is a membrane-bound protein that functions in bacterial adhesion and promotes the formation of aggregates that are lethal to the insect host. These results illustrate that the enteric plant pathogenic bacteria have the capacity to exploit alternative non-plant hosts, and retain genetic determinants for colonizing the gut.