The relative toxicity of a spore preparation of Bacillus thuringiensis var. israelensis against fourth instar larvae of Aedes aegypti and Toxorhynchites amboinensis: suspension feeding compared with enemas and forced feeding

The toxic effect of a spore preparation of Bacillus thuringiensis var. israelensis Berliner Serotype H-14 (Bti) on 4th instar larvae of Aedes aegypti L. and Toxorhynchites amboinensis (Doleschall) was observed when given either in a suspension feeding test or when injected orally as a forced feeding or via the anus as an enema. The A. aegypti larvae showed the greater sensitivity to Bti both because they greatly concentrate the toxin by filter feeding and they are more sensitive to Bti than are the larvae of T. amboinensis. The latter appeared approximately two-fold less sensitive to Bti than the former after taking into account their greater body weight.

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Résumé La toxicité sur des larves de 4ème stade de A. aegypti et T. amboinensis, d'une préparation de spores de B. thuringiensis var. israelensis Berliner sérotype H-14, a été examinée après: injection orale par alimentation forcée, injection anale comme lavement, — le témoin étant une alimentation à partir d'une suspension de spores.Les larves de A. aegypti ont présenté la plus grande sensibilité au Bti d'une part parce qu'elles concentrent beaucoup la toxine avec leur alimentation par filtration, et parce qu'elles sont plus sensibles sensu stricto au Bti. Même en tenant compte de leur poids plus élevé, T. amboinensis est apparu comme deux fois moins sensible au Bti.

     

Characterization of base-pair opening in deoxynucleotide duplexes using catalyzed exchange of the imino proton

Using nuclear magnetic resonance line broadening, longitudinal relaxation and magnetization transfer from water, we have measured the imino proton exchange times in the duplex form of the 10-mer d-CGCGATCGCG and in seven other deoxy-duplexes, as a function of the concentration of exchange catalysts, principally ammonia. All exchange times are catalyst dependent. Base-pair lifetimes are obtained by extrapolation to infinite concentration of ammonia. Lifetimes of internal base-pairs are in the range of milliseconds at 35 degrees C and ten times more at 0 degrees C. Lifetimes of neighboring pairs are different, hence base-pairs open one at a time. Lifetimes of d(G.C) are about three times longer than those of d(A.T). The nature of neighbors usually has little effect, but lifetime anomalies that may be related to sequence and/or structure have been observed. In contrast, there is no anomaly in the A.T base-pair lifetimes of d-CGCGA[TA]5TCGCG, a model duplex of poly[d(A-T)].poly[d(A-T)]. The d(A.T) lifetimes are comparable to those of r(A.U) that we reported previously. End effects on base-pair lifetimes are limited to two base-pairs. The low efficiency of exchange catalysts is ascribed to the small dissociation constant of the deoxy base-pairs, and helps to explain why exchange catalysis had been overlooked in the past. This resulted in a hundredfold overestimation of base-pair lifetimes. Cytosine amino proteins have been studied in the duplex of d-CGm5CGCG. Exchange from the closed base-pair is indicated. Hence, the use of an amino exchange rate to evaluate the base-pair dissociation constant would result in erroneous, overestimated values. Catalyzed imino proton exchange is at this time the safest and most powerful, if not the only probe of base-pair kinetics. We propose that the single base-pair opening event characterized here may be the only mode of base-pair disruption, at temperatures well below the melting transition.     

Dipeptidyl-amino-peptidase IV activity in stored buffy coat smears from human blood

The stability of dipeptidyl-amino-peptidase IV (DAP IV) activity in lymphoid cells of buffy coat smears from human blood was studied during storage for 40 days. Fixed or unfixed smears may be stored at 20 C for up to 24 hr before a decrease in activity occurs. Storage of either fixed or unfixed smears at 4 C, -10 C and -80 C results in a significant loss of activity within 24 hr. However, the cells retain more than 85% of their DAP IV activity for up to 10 days when stored fixed at -80 C. These data underscore the importance of proper processing of slides for DAP IV staining to avoid misinterpretation of results.     

DNA sequence of a class I pseudogene from theTla region of the murine MHC: Recombination at a B2 Alu repetitive sequence

Summary We have determined the DNA sequence of a BALB/cTla region class I gene from the major histocompatibility complex (MHC) that had been identified previously as encoding a murine antigen by DNA-mediated gene transfer. Analysis of the DNA sequence shows, however, that this gene, the T1^c gene from theTla ^c genotype, could not encode a TL antigen or any other functional class I molecule due to the presence of numerous stop codons and frameshift mutations in the coding regions. This result suggests that the earlier transformation data may have been incorrect or perhaps that the clone containing the T1^c gene contains sequences that induced expression of a serologically reactiveTla gene in the genome of the recipient L cell. The T1^c gene is structurally related to the previously sequenced T13^c gene that encodes a serologically defined TL antigen. The 3 half of the T1^c gene including exons 4, 5, 6, and the 3 untranslated region has about 85% nucleotide similarity (including introns) with the corresponding parts of the T13^c gene; however, the 5 half of the T1^c gene has little homology with the T13^c gene. There is a sharp line of demarcation between the homologous and nonhomologous regions, and this border occurs precisely at a B2 Alu repeat sequence present in the T13^c gene. This suggests that a recombination event took place here and that an Alu repeat sequence that is known to have characteristics of transposable elements played some role in a recombination or gene conversion event.     

Biochemical and spectroscopic characterization of the high molecular weight cytochrome c from Desulfovibrio vulgaris Hildenborough expressed in Desulfovibrio desulfuricans G200.

The gene of high molecular weight, multiheme cytochrome c (Hmc) from the sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough has been overexpressed in Desulfovibrio desulfuricans G200. The recombinant protein has been purified. Its molecular weight (65,600), amino acid composition, and NH2-terminal sequence were found to be identical to those of the wild-type protein. The recombinant protein has been spectroscopically characterized (optical spectrum, EPR, circular dichroism) and compared to the wild-type protein. We have found 16 hemes per molecule by iron analysis and the pyridine hemochrome test. Both high- and low-spin features were observed in the EPR spectrum. A detailed spin quantitation analysis indicates 1 or 2 high-spin hemes and 14 or 15 low-spin hemes per molecule. The redox potentials of the hemes determined by voltammetric techniques gave an average of three different values, 0, -100, and -250 mV (versus NHE), for the wild-type and the recombinant cytochrome. The low potential values are similar to the values observed for the bis(histidinyl) coordinated hemes of cytochrome c3. A comparison of the arrangement of heme binding sites and coordinated histidines in the amino acid sequences of cytochrome c3 and Hmc has shown that the latter contains four domains, three of which are complete c3-like domains, while the fourth represents an incomplete c3-like domain which may contain His-Met coordinated hemes. These data are in agreement with the detailed study of the number and types of hemes reported in this paper.