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Biomedical subjects

A Peleg

Publications and source records attributed to A Peleg.

6 recordsLinked to original sources
PubMed1992

A cis-acting DNA signal for encapsidation of simian virus 40.

Encapsidation of simian virus 40 is a complex biological process involving DNA-protein and protein-protein interactions in the formation of a unique three-dimensional structure around the viral minichromosome. A pseudoviral system developed in our laboratory, in which the viral early and late gene products are supplied in trans (by helpers), was used to analyze the encapsidation process independent of viral gene expression. With this experimental system we have discovered a requirement for a specific DNA signal for encapsidation, ses (for simian virus 40 encapsidation signal).ses is present within a 200-bp DNA fragment, which includes, in addition to the viral origin of replication (ori), six GGGCGG repeats (GC boxes) and 26 bp of the enhancer element. Deletion of the GC boxes and the enhancer sequences almost abolished encapsidation, while DNA replication was only moderately decreased. The ability to encapsidate was not regained by reinserting a DNA fragment carrying ses in the sesdeleted plasmid 2 kbp away from the ori, suggesting that for encapsidation the two DNA elements have to be close to each other. These findings afford novel strategies for the investigation of viral encapsidation.

Animals↗
PubMed1989

Helpers for efficient encapsidation of SV40 pseudovirions.

Plasmid DNA that carries the simian virus 40 (SV40) ori can be packaged as SV40 pseudovirions. The pseudovirions are very efficient in gene transmission into a variety of cell types, including human hemopoietic cells. They are routinely prepared with wild-type (wt) SV40 as a helper. In the present study, several parameters required for the helper function were investigated. Plasmids that carry pBR322 sequences in addition to the late genes of SV40 were inefficient in providing helper functions, presumably because the prokaryotic sequences interfered with expression of the SV40 late genes. Efficient helpers were plasmid pSVPiC [Villarreal and Soo, Mol. Appl. Genet. 3 (1985) 62-71] and an SV40 defective virus SLT3 (presently constructed). Plasmid pSVPiC carries a duplication of the SV40 ori and enhancer regions, and pi AN7 sequences. Because of its large size it was not packaged into virion particles. However, it underwent extensive recombination generating infective SV40 particles. Almost no prokaryotic sequences are included in SLT3, that carries the SV40 late gene. In spite of its small size (3.5 kb) it was packaged efficiently, creating defective (T-antigen-negative) SV40 virions. The availability of T-antigen positive and negative pseudovirion mixtures enabled us to suggest that T-antigen drives gene amplification in the target human hemopoietic cells.

Animals↗
PubMed1986

Efficient introduction of plasmid DNA into human hemopoietic cells by encapsidation in simian virus 40 pseudovirions.

Introduction of DNA into human hemopoietic cells is required for the study of regulatory mechanisms operating in these cells, as well as for possible procedures of gene therapy. However, with hemopoietic cells the conventional technique of calcium phosphate precipitation is inefficient. The pathway of encapsidation of plasmid DNA as simian virus 40 (SV40) pseudovirions for the introduction of new genetic material was therefore investigated. Encapsidation was achieved in COS (monkey kidney) cells, which express SV40 large tumor (T) antigen constitutively. The vector, pSO, was introduced to the COS cells by DNA transfection. It carried the SV40 origin of replication (ori), to facilitate replication of the plasmid in the COS cells. The SV40 capsid proteins were supplied in trans by a helper SV40 virus. The bacterial chloramphenicol acetyltransferase gene cat was used as a model for gene transmission. After encapsidation, the pseudovirions were used in infection of the human erythroleukemic cell line K562 and of normal human bone marrow cells. The results demonstrate that the cat gene can be transmitted with high efficiency. Over 40% of the infected K562 cells and 30% of the infected bone marrow cells were observed to contain plasmid DNA 48 hr after infection. Moreover, the results suggest that the efficiency of gene transmission by this vector can be improved and so may approach the theoretical 100%.

Acetyltransferases↗
PubMed1978

Embolization of detached fragments of intravenous plastic catheter.

Three cases of embolization by detached fragments of "Intracath" intravenous catheters are described. In two, successful surgical removal was performed, whilst in the third, due to the poor general condition of the patient, no attempt at removal was made and after long-term observation, there were no untoward side effects.

Adult↗
PubMed1977

Automatic testing of the visual field using electro-oculographic potentials.

The central visual field is tested using static perimetry on a tangent screen located 1 m from the patient. During the test electro-oculographic (EOG) potentials, associated with eye movements, are recorded. For this purpose two pairs of electrodes are placed in such a way that one pair records the vertical and the other the horizontal component of the EOG potential. The EOG signals that are produced when the tested eye moves toward the light target on the screen are digitized and fed into a computer programmed to relate each pair of signals to the specific lamp on the tangent screen. The results of the test appear on a computer-printed chart that shows the distribution of the lamps on the testing board together with the information whether the lamp was seen by the subject. This method of visual field testing is both objective and automatic.

Automation↗