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1.
Molecular genetic maps are commonly constructed by analyzing the segregation of restriction fragment length polymorphisms (RFLPs) among the progeny of a sexual cross. Here we describe a new DNA polymorphism assay based on the amplification of random DNA segments with single primers of arbitrary nucleotide sequence. These polymorphisms, simply detected as DNA segments which amplify from one parent but not the other, are inherited in a Mendelian fashion and can be used to construct genetic maps in a variety of species. We suggest that these polymorphisms be called RAPD markers, after Random Amplified Polymorphic DNA.  相似文献
2.
Sequential human immunodeficiency virus (HIV) isolates, recovered from a panel of longitudinally collected peripheral blood mononuclear cells obtained from 20 initially asymptomatic HIV-seropositive homosexual men, were studied for differences in replication rate, syncytium-inducing capacity, and host range. Eleven individuals remained asymptomatic; nine progressed to acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) at the time point at which the last HIV isolate was obtained. In 16 individuals, only non-syncytium-inducing (NSI) isolates, with a host range restricted to mononuclear cells, were observed. From four individuals, high-replicating, syncytium-inducing (SI) isolates that could be transmitted to the H9, RC2A, and U937 cell lines were recovered. From two of these four individuals, SI isolates were obtained throughout the observation period. In the two others, a transition from NSI to SI HIV isolates was observed during the period of study. Three of these four individuals developed ARC or AIDS 9 to 15 months after the first isolation of an SI isolate. With the exception of the two individuals in whom a transition from NSI to SI isolates was observed, within a given individual the replication rate of sequential HIV isolates was constant. A significant correlation was found between the mean replication rate of isolates obtained from an individual and the rate of CD4+ cell decrease observed in this individual. In individuals with low-replicating HIV isolates, no significant CD4+ cell loss was observed. In contrast, recovery of high-replicating isolates, in particular when these were SI isolates, was associated with rapid decline of CD4+ cell numbers and development of ARC or AIDS. These findings indicate that variability in the biological properties of HIV isolates is one of the factors influencing the course of HIV infection.  相似文献
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The composition of human immunodeficiency virus type 1 (HIV-1) clonal populations at different stages of infection and in different compartments was analyzed. Biological HIV-1 clones were obtained by primary isolation from patient peripheral blood mononuclear cells under limiting dilution conditions, with either blood donor peripheral blood lymphocytes or monocyte-derived macrophages (MDM) as target cells, and the biological phenotype of the clones was analyzed. In asymptomatic individuals, low frequencies of HIV-1 clones were observed. These clones were non-syncytium inducing and preferentially monocytotropic. In individuals progressing to disease, a 100-fold increase in frequencies of productively HIV-1-infected cells was observed as a result of a selective expansion of nonmonocytotropic clones. In a person progressing to AIDS within 19 months after infection, only syncytium-inducing clones were detected, shifting from MDM-tropic to non-MDM-tropic over time. From his virus donor, a patient with wasting syndrome, only syncytium-inducing clones, mostly non-MDM-tropic, were recovered. Parallel clonal analysis of HIV-1 populations in cells present in bronchoalveolar lavage fluid and peripheral blood from an AIDS patient revealed a qualitatively and quantitatively more monocytotropic virus population in the lung compartment than in peripheral blood at the same time point. These findings indicate that monocytotropic HIV-1 clones, probably generated in the tissues, are responsible for the persistence of HIV-1 infection and that progression of HIV-1 infection is associated with a selective increase of T-cell-tropic, nonmonocytotropic HIV-1 variants in peripheral blood.  相似文献
5.
Human immunodeficiency virus isolates were studied with respect to syncytium-inducing capacity, replicative properties, and host range. Five of 10 isolates from patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex were able to induce syncytia in cultures of peripheral blood mononuclear cells (MNC). In contrast, only 2 of 12 isolates from asymptomatic individuals had syncytium-inducing capacity. Syncytium-inducing isolates were reproducibly obtained from the same MNC sample in over 90% of the cases, independent of the donor MNC used for propagation. Syncytium-inducing capacity was shown to be a stable property of an isolate, independent of viral replication rates. Evidence was obtained that the high replication rate of syncytium-inducing isolates observed during primary isolation may be due to higher infectivity of these isolates. The finding that only syncytium-inducing isolates could be transmitted to the H9 cell line is compatible with this higher infectivity. The frequent isolation of syncytium-inducing isolates from individuals with AIDS-related complex or AIDS and the apparent higher in vitro infectivity of these isolates suggest that syncytium-inducing isolates may unfavorably influence the course of human immunodeficiency virus infection.  相似文献
6.
The abilities of 18 synthetic peptides to target a carrier protein to the nucleus following microinjection into the cytoplasm of HeLa cells were determined. Eight of the sequences chosen for synthesis were based on published nuclear targeting regions as determined by gene fusion and deletion experiments. Six of these sequences were found to be effective when mimicked by a synthetic peptide and conjugated to a carrier protein. One additional peptide was based on a region of lamin L1, a nuclear protein from Xenopus laevis, in which the nuclear targeting region had not been previously investigated. This peptide was also able to target a carrier protein to the nucleus. Eight other peptides which resemble the known targeting signals had little or no nuclear targeting ability. Peptides which were able to target a carrier protein to the nucleus did so within 45 min of injection into the cytoplasm. Two peptides with little or no apparent nuclear targeting ability after 45 min were examined for longer times as well. No increase in nuclear accumulation was observed between 45 min and 4 h after cytoplasmic injection. Comparison of the sequences which were effective at nuclear targeting with those that were not revealed a possible consensus sequence for peptide-mediated nuclear transport.  相似文献
7.
Lipoproteins in bacteria   总被引:78,自引:0,他引:78  
Covalent modification of membrane proteins with lipids appears to be ubiquitous in all living cells. The major outer membrane (Braun's) lipoprotein ofE. coli, the prototype of bacterial lipoproteins, is first synthesized as a precursor protein. Analysis of signal sequences of 26 distinct lipoprotein precursors has revealed a consensus sequence of lipoprotein modification/processing site of Leu-(Ala, Ser)-(Gly, Ala)-Cys at – 3 to + 1 positions which would represent the cleavage region of about three-fourth of all lipoprotein signal sequences in bacteria. Unmodified prolipoprotein with the putative consensus sequence undergoes sequential modification and processing reactions catalyzed by glyceryl transferase, O-acyl transferase(s), prolipoprotein signal peptidase (signal peptidase II), and N-acyl transferase to form mature lipoprotein. Like all exported proteins, the export of lipoprotein requires functional SecA, SecY, and SecD proteins. Thus all precursor proteins are exported through a common pathway accessible to both signal peptidase I and signal peptidase II. The rapidly increasing list of lipid-modified proteins in both prokaryotic as well as eukaryotic cells indicates that lipoproteins comprise a diverse group of structurally and functionally distinct proteins. They share a common structural feature which is derived from a common biosynthetic pathway.  相似文献
8.
Features of promising technologies for pretreatment of lignocellulosic biomass   总被引:76,自引:0,他引:76  
Cellulosic plant material represents an as-of-yet untapped source of fermentable sugars for significant industrial use. Many physio-chemical structural and compositional factors hinder the enzymatic digestibility of cellulose present in lignocellulosic biomass. The goal of any pretreatment technology is to alter or remove structural and compositional impediments to hydrolysis in order to improve the rate of enzyme hydrolysis and increase yields of fermentable sugars from cellulose or hemicellulose. These methods cause physical and/or chemical changes in the plant biomass in order to achieve this result. Experimental investigation of physical changes and chemical reactions that occur during pretreatment is required for the development of effective and mechanistic models that can be used for the rational design of pretreatment processes. Furthermore, pretreatment processing conditions must be tailored to the specific chemical and structural composition of the various, and variable, sources of lignocellulosic biomass. This paper reviews process parameters and their fundamental modes of action for promising pretreatment methods.  相似文献
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