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Biomedical subjects

L F Cavalieri

Publications and source records attributed to L F Cavalieri.

At least 19 recordsLinked to original sources
PubMed1995

Chaos: a potential problem in the biological control of insect pests.

Erratic variations are normally observed in the populations of insect pests that destroy crop plants. To establish a scientific basis for developing effective control procedures, we have developed a model system for the European Corn Borer (ECB) (Ostrinia nubilalis) for which extensive field data, as well as laboratory results, have been accumulated during the past four decades. The model includes both a natural ECB pathogen and a genetically engineered toxin-producing agent as possible means of biological control. Our aim was to determine the conditions that could cause the population to vary erratically, as observed in the field. The erratic behavior in our simulations was analyzed to determine whether it is chaotic; chaos is a distinct type of erratic behavior which shows extreme sensitivity to initial conditions, i.e., the starting size of the population. Our simulations show that an increase in the death rate of the infected ECB, or a decrease in the birth rate of uninfected ECBs from infected ones, variables that are known to be affected by weather conditions, can induce a chaotic regime in which ECB population peaks reach values far higher than before chaos set in. Population peaks are even greater in the presence of both biological control agents. The results show that a biological control regime cannot be effective under conditions that induce chaotic population dynamics. Microcosm studies could be used to determine whether this situation would occur in the field.

Animals↗
PubMed1986

Inhibition of SV40 DNA replication by benzo[a]pyrene diol epoxide adducts: two recovery modes.

Anti-benzo[a]pyrene diol epoxide (BPDE) adducts produced in vitro in SV40 initially inhibit SV40 DNA replication in vivo, in cells unexposed to BPDE. A single adduct in a replicon is probably sufficient to block DNA replication. The recovery process appears to begin immediately after infection. The rate of recovery of replicative capacity is inversely related to the initial adduct number. Holding the infected cells temporarily under conditions that prevent viral DNA replication results subsequently in increased recovery, proportional to the holding time. The mechanism of recovery appears to be constitutive and prereplicative. In addition, there is a second mode of recovery which is induced by pretreatment of the host cells with BPDE before infection. The effect of pretreatment is similar to that of extending the holding time before replication: the first molecules begin to replicate earlier but the subsequent rate of recovery is unchanged. The induced mechanism may be either a limited stoichiometric repair process or a slow replicative bypass.

Animals↗
PubMed1982

Termination of DNA synthesis in vitro at apurinic sites but not at ethyl adducts on the template.

The effects of DNA lesions produced by the carcinogenic alkylating agents ethylnitrosourea and diethylsulfate on the extent of DNA synthesis have been studied in a system utilizing circular single-stranded phiX174 DNA as template and a 392-base restriction fragment as primer with E. coli polymerase I (Klenow fragment). Apurinic sites produced by loss of unstable ethylated bases from the template terminate DNA synthesis at the first such site encountered, but ethyl adducts at most, if not all, locations permit readthrough.

DNA Replication↗
PubMed1981

The major adducts of cis and trans benzo[a]pyrene diol epoxides cause chain termination during DNA synthesis in vitro.

We have studied DNA synthesis in vitro using as template phi X174 DNA containing varying numbers of adducts formed by reaction with cis and trans benzo[a]pyrene (BP) diol-epoxides. The extent of DNA synthesis decreases with increasing numbers of adducts and there is a concomitant decrease in the size of the DNA products. Both decreases can be accounted for quantitatively by the assumption that synthesis terminates at every BP adduct. Since the majority of the adducts are located at the 2-amino group of guanine, we deduce that these adducts cause termination. The role of adducts at other sites is uncertain. The cis and trans BP diol-epoxides are indistinguishable with regard to chain termination, yet in vivo these isomers behave differently. These results suggest that chain determination alone is insufficient to account for the mutagenic effects of BP diol-epoxides.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1981

Effects of ethylating agents on DNA synthesis in vitro: implications for the mechanism of carcinogenesis.

A highly carcinogenic ethylating agent, ethylnitrosourea (ENU), and a weakly carcinogenic one, diethylsulfate (DES) react with DNA to roughly the same extent but DES produces about 6 times as many unstable ethylated bases, which are gradually lost spontaneously under physiological conditions. The different rates of loss for the different DNA bases have been studied using polydeoxyribonucleotides. Spontaneous strand breakage following base loss is slow, lagging more than a week behind base loss at 37 degrees C; ultimately, DES results in much more spontaneous strand breakage than ENU. In DNA synthesis in vitro, using avian myeloblastosis virus (AMV) polymerase, no nucleotides are incorporated opposite missing bases in the template; when the template contains ethylated bases that are impaired in their ability to form specific hydrogen bonds, purine-pyrimidine mispairing can occur and mismatched nucleotides are incorporated into the daughter strand. ENU ethylates somewhat more sites leading to mispairing potential than DES. ENU also produces approximately 7.5 times more ethyl phosphotriesters than DES.

Alkylating Agents↗
PubMed1978

Effects of benzo(a)pyrene adducts of DNA synthesis in vitro.

Two diol epoxides of benzo(a)pyrene (BP), and benzo(a)pyrene 4,5-oxide, have been used to make adducts in the homopolymers polyribocytidylic acid, (rC); polyriboadenylic acid (rA), polydeoxycytidylic acid (dC) and polydeoxyadenylic acid (dA). With appropriate oligomers as primers these modified and unmodified polynucleotides were used as templates for DNA synthesis with avian myeloblastosis virus DNA polymerase (AMV) or E. coli Pol I DNA polymerase. We have found that: (1) the size of the DNA product is not markedly decreased by the presence of these these polycyclic aromatic hydrocarbon adducts in the templates; (2) the presence of adducts does not lead to increased incorporation of erroneous bases. These results, supported by kinetic data, suggest that these polymerases can bypass a site containing an adduct on the template without leaving a gap or causing misincorporation of a base and they imply that mutagenesis by BP may not be attributable to either of these mechanisms.

Avian Myeloblastosis Virus↗
PubMed1978

Inhibition of reverse transcription of 70S and 35S avian myeloblastosis RNAs by nonprimer tRNA's.

We studied the kinetics of the reverse transcription of 70S and 35S RNA of avian myeloblastosis virus in the presence and absence of various tRNA's. All tRNA's inhibited synthesis. tRNA's from Escherichia coli and yeast exhibited a noncompetitive type of inhibition, i.e., they bound reversibly and randomly and did not alter the affinity of the viral RNA for the polymerase. Nonprimer tRNA's obtained from 70S RNA molecules produced a complex pattern of inhibition. The results show that the nonprimer tRNA's which bound to the reverse transcriptase decreased the affinity of the viral RNA for the enzyme. The maximum rate of synthesis with 70S RNA as the template was less than that with 35S RNA, presumably because the former contains nonprimer tRNA's which can interact with the polymerase.

Avian Leukosis Virus↗
PubMed1977

Characterization of a DNA polymerase associated with an endogenous DNA-synthesizing complex isolated from human lymphoid cells.

We have shown that a membrane fraction prepared from isolated human lymphoid nuclei contains endogenous DNA-synthesizing activity which is sensitive to RNAase. We have isolated a DNA polymerase from this fraction and partially purified it to what we estimate as about 10 000-fold. Its chromatographic behavior, template specificity, sedimentation constant, pH optimum, and sensitivity to N-ethylmaleimide suggest that the activity resembles but is not identical to DNA polymerase gamma (formerly called R-DNA polymerase). The membrane fraction also contains a minor activity which is due to polymerase beta, the low molecular weight (3.5 S) nuclear enzyme.

Cell Line↗
PubMed1976

Mechanism of interaction of avian myeloblastosis virus reverse transcriptase with avian myeloblastosis virus RNA.

The synthesis of DNA on avian myeloblastosis virus (AMV) RNA as the primer-template using AMV reverse transcriptase in vitro has been examined as a function of the concentrations of these components, as well as a function of the ionic strenth of the assay medium. The results are consistent with the hypothesis that two types of sites exist on the AMV RNA: inactive "dead-end" sites that merely bind the enzyme, and active binding sites that lead to DNA synthesis. Velocity sedimentation studies of reverse transcriptase reveal that the enzyme becomes a dimer (or oligomer) at low salt concentrations and it is at these concentrations that the two types of sites are evident on the RNA. At high salt concentration the enzyme, which exists primarily as a monomer, is inactive with AMV RNA, although it is active when poly(rA)dT10 is used as the primer-template. We have shown that inactive sites are not due to binding of the reverse transcriptase to nicked regions or to partially denatured RNA molecules. We deduce that inactive sites are those containing incorrect 4S primer molecules. These results are discussed in terms of the mechanism of the interaction of the reverse transcriptase with AMV RNA.

Avian Leukosis Virus↗
PubMed1975

E. coli tRNAs as inhibitors of viral reverse transcription in vitro.

Reverse transcription of 70S AMV RNA by AMV reverse transcriptase has been studied in the presence of E. coli tRNAs. We have shown that inhibition of DNA synthesis occurs and that the tRNAs bind to the enzyme and not to the 70S RNA. The results have implications for the control of reverse transcription in vivo.

Avian Myeloblastosis Virus↗
PubMed1975

In vitro DNA synthesis on smooth membranes observed by fluorescence.

Smooth membranes have been isolated from a human diploid line of lymphocytes. These membranes exhibit an endogenous DNA-synthesizing capability which is partially destroyed by prior treatment with RNase. In order to ascertain the role of the membranes in the DNA synthesis we have examined the conformation of the membrane proteins by observing fluorescence changes of the intrinsic probe, tryptophan. We have observed that on addition of the deoxynucleoside-5'-triphosphates, which permits DNA synthesis, there are fluorescence changes due to the tryptophan residue; when DNA synthesis is prevented by omitting some of the precursor triphosphates, fluorescence changes are absent. These effects have been observed with plasma and nuclear membrane fractions; the former may contain a small fraction of the latter. Similar membrane preparations from non-lymphoid cells do not process the endogenous DNA-synthesizing system, as shown by the lack of incorporation of radioactive precursors of fluorescence changes.

Cell Line↗
PubMed1974

Evidence for allosterism in in vitro DNA synthesis on RNA templates.

Hemoglobin mRNA and (rA)(n).(dT)(10) have been used as primer-templates in a kinetic study of DNA synthesis with Escherichia coli DNA polymerase I (DNA nucleotidyl transferase, EC 2.7.7.7) and Mason-Pfizer monkey virus reverse transcriptase (RNA-directed DNA polymerase). The rate versus enzyme concentration curve is sigmoidal and is consistent with a cooperative phenomenon. The results could be interpreted in terms of the formation of an active complex containing enzyme dimers (or oligomers) on the primer-template. We have also observed sigmoidal kinetics in rate versus deoxynucleotide triphosphate concentration. These results are consistent with an allosteric mechanism in which the triphosphates act as both modifiers and DNA precursors. In the critical range, a 6- to 8-fold increase in both enzyme and triphosphate concentrations can lead to a 1500-fold increase in the rate of synthesis on an RNA template. Thus, small changes in enzyme and precursor concentrations could play a regulatory role in vivo.

Adenosine Triphosphate↗
PubMed1974

Purification of avian myeloblastosis virus DNA polymerase by affinity chromatography on polycytidylate-agarose.

Polycytidylic acid [poly(rC)] covalently linked to cyanogen bromide-activated agarose is an effective affinity matrix for the RNA-dependent DNA polymerase from avian myeloblastosis virus. Poly(rC)-agarose is capable of binding large quantities of avian myeloblastosis DNA polymerase, which is then eluted by using a linear KCl gradient of increasing concentration. The DNA polymerase isolated from crude, detergent-disrupted virions by a single pass through columns of poly(rC)-agarose appears nearly homogeneous (approximately 90% pure) as determined by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complete recovery of input enzymatic activity was obtained. Results suggest that polyribonucleotide columns may provide a high-yield, rapid method for the purification of oncornaviral DNA polymerase.

Avian Leukosis Virus↗