Single strand conformational polymorphism evaluation for the identification of TH3R alleles of the circumsporozoite protein gene of Plasmodium falciparum

Highly polymorphic regions of the circumsporozoite protein (CSP) of Plasmodium falciparum are associated with cellular immune responses. One of these regions, the TH3R polymorfic region of the csp gene codes for known T-cell epitopes. The present study tested the use of SSCP to determine sequence variations of the TH3R regions of four clones of P. falciparum (3D7, HB3, Dd2 and K1) which are known to have different TH3R regions. Single-strand conformation polymorphism (SSCP) technique was performed on amplified products labelled with fluorescent primer (both strands) and electrophoresed in an automated sequencer. Various gel compositions and electrophoresis conditions were tested. Even if some electrophoretogram differences were observed between clones, they could not distinguish between the alleles.     

Sinorhizobium fredii HH103 has a truncated nolO gene due to a -1 frameshift mutation that is conserved among other geographically distant S. fredii strains

Strain SVQ121 is a mutant derivative of Sinorhizobium fredii HH103 carrying a transposon Tn5-lacZ insertion into the nolO-coding region. Sequence analysis of the wild-type gene revealed that it is homologous to that of Rhizobium sp. NGR234, which is involved in the 3 (or 4)-O-carbamoylation of the nonreducing terminus of Nod factors. Downstream of nolO, as in Rhizobium sp. NGR234, the noeI gene responsible for methylation of the fucose moiety of Nod factors was found. SVQ121 Nod factors showed lower levels of methylation into the fucosyl residue than those of HH103-suggesting a polar effect of the transposon insertion into nolO over the noel gene. A noeI HH103 mutant was constructed. This mutant, SVQ503, produced Nod factors devoid of methyl groups, confirming that the S. fredii noeI gene is functional. Neither the nolO nor the noeI mutation affected the ability of HH103 to nodulate several host plants, but both mutations reduced competitiveness to nodulate soybean. The Nod factors produced by strain HH103, like those of other S. fredii isolates, lack carbamoyl residues. By using specific polymerase chain reaction primers, we sequenced the nolO gene of S. fredii strains USDA192, USDA193, USDA257, and 042B(s). All the analyzed strains showed the same -1 frameshift mutation that is present in the HH103 nolO-coding region. From these results, it is concluded that, regardless of their geographical origin, S. fredii strains carry the nolO-coding region but that it is truncated by the same base-pair deletion.     

Study of the biological effects and DNA damage exerted by a new dipalladium-Hmtpo complex on human cancer cells

The new dipalladium complex [Pd(2)(mu-mtpo-N(3),N(4))(2)(phen)(2)](NO(3))(2) (where phen=1,10-phenantroline; Hmtpo=5,7-dihydro-7-oxo-5-methyl[1,2,4]triazolopyrimidine), (Pd(2)-Hmtpo, or complex I), interacts effectively with DNA plasmid (pBS), as studied by circular dichroism spectroscopy (CD), causing large helix distortions, altering the direction of the main DNA helix axis and producing unwinding of the DNA double helix. DNA damage induced by complex I was highly significant at 2.81 microM (ovarian carcinoma TG cell line), as assessed by comet assay, a dose at which all treated nuclei showed more than 30% DNA migration to the comet tail. DNA damage effect is a consequence of genotoxicity and not a false positive response caused by cytotoxicity. In vitro cytotoxic assay on the two human tumor cell lines TG and BT-20 (breast carcinoma), shows that doses of 0.47, 1.41 and 2.81 microM produce significant antiproliferative effects after 4 days of treatment compared with control. Complex I was highly cytotoxic at 2.81 microM causing an inhibition of viable cells of 65.5%. Cisplatin (cis-DDP) exhibits lower cytotoxic activity in TG cells than dipalladium complex (a cisplatin dose of 6.67 microM inhibits 30.3%) and does not cause migration of DNA to comet tail.     

Characterization of salt stress-enhanced phosphoenolpyruvate carboxylase kinase activity in leaves of <Emphasis Type="Italic">Sorghum</Emphasis><Emphasis Type="Italic">vulgare</Emphasis>: independence from osmotic stress,involvement of ion toxicity and significance of dark phosphorylation

C(4) phosphoenolpyruvate carboxylase (PEPCase: EC 4.1.1.31) is subjected to in vivo regulatory phosphorylation by a light up-regulated, calcium-independent protein kinase. Salt stress greatly enhanced phosphoenolpyruvate carboxylase-kinase (PEPCase-k) activity in leaves of Sorghum. The increase in PEPCase-k anticipated the time course of proline accumulation thereby suggesting that water stress was not involved in the kinase response to salt. Moreover, osmotic stress seemed not to be the main factor implicated, as demonstrated by the lack of effect when water availability was restricted by mannitol. In contrast, LiCl (at a concentration of 10 mM in short-term treatment of both excised leaves and whole plants) mimicked the effects of 172 mM NaCl salt-acclimation, indicating that the rise in PEPCase-k activity resulted primarily from the ionic stress. Both NaCl and LiCl treatments increased the activity of a Ca(2+)-independent, 35 kDa kinase, as demonstrated by an in-gel phosphorylation experiment. Short-term treatment of excised leaves with NaCl or LiCl partially reproduces the effects of whole plant treatments. Finally, salinization also increased PEPCase-k activity and the phosphorylation state of PEPCase in darkened Sorghum leaves. This fact, together with increased malate production during the dark period, suggests a shift towards mixed C(4) and crassulacean acid metabolism types of photosynthesis in response to salt stress.     

'A mate or a meal' – Pre-gravid behaviour of female Anopheles gambiae from the islands of São Tomé and Príncipe, West Africa

Background

The spread of drug resistance is making malaria control increasingly difficult. Mathematical models for the transmission dynamics of drug sensitive and resistant strains can be a useful tool to help to understand the factors that influence the spread of drug resistance, and they can therefore help in the design of rational strategies for the control of drug resistance.

Methods

We present an epidemiological framework to investigate the spread of anti-malarial resistance. Several mathematical models, based on the familiar Macdonald-Ross model of malaria transmission, enable us to examine the processes and parameters that are critical in determining the spread of resistance.

Results

In our simplest model, resistance does not spread if the fraction of infected individuals treated is less than a threshold value; if drug treatment exceeds this threshold, resistance will eventually become fixed in the population. The threshold value is determined only by the rates of infection and the infectious periods of resistant and sensitive parasites in untreated and treated hosts, whereas the intensity of transmission has no influence on the threshold value. In more complex models, where hosts can be infected by multiple parasite strains or where treatment varies spatially, resistance is generally not fixed, but rather some level of sensitivity is often maintained in the population.

Conclusions

The models developed in this paper are a first step in understanding the epidemiology of anti-malarial resistance and evaluating strategies to reduce the spread of resistance. However, specific recommendations for the management of resistance need to wait until we have more data on the critical parameters underlying the spread of resistance: drug use, spatial variability of treatment and parasite migration among areas, and perhaps most importantly, cost of resistance.     

Three maize root-specific genes are not correctly expressed in regenerated caps in the absence of the quiescent center

The quiescent center is viewed as an architectural template in the root apical meristem of all angiosperm and gymnosperm root tips. In roots of Arabidopsis thaliana (L.) Heynh., the quiescent center inhibits differentiation of contacting initial cells and maintains the surrounding initial cells as stem cells. Here, the role of the quiescent center in the development of the maize (Zea mays L.) root cap has been further explored. Three maize root-specific genes were identified. Two of these were exclusively expressed in the root cap and one of them encoded a GDP-mannose-4,6-dehydratase. Most likely these two genes are structural, tissue-specific markers of the cap. The third gene, a putative glycine-rich cell wall protein, was expressed in the cap and in the root epidermis and, conceivably is a positional marker of the cap. Microsurgical and molecular data indicate that the quiescent center and cap initials may regulate the positional and structural expression of these genes in the cap and thereby control root cap development. Received: 22 September 1999 / Accepted: 9 November 1999