Search PubMed⌕ Search

Biomedical subjects

P Berg

Publications and source records attributed to P Berg.

At least 253 records · Page 14Linked to original sources
PubMed1976

Construction of hybrid viruses containing SV40 and lambda phage DNA segments and their propagation in cultured monkey cells.

This paper describes the successful construction and propagation of a transducing animal virus. A segment of DNA approximately 2 kilobases (kb) in length was removed from the late region of the SV40 genome by sequential cleavages with Hpa II and Bam HI endonucleases (at 0.735 and 0.13, respectively, on the SV40 DNA map). A segment of about 1.5 kb of lambda phage containing ORI (the origin of lambda DNA replication), the two structural genes CII and cro, and four transcriptional promoters, was inserted into the late region of SV40 by the poly(dA:dT) joining procedure. The resulting hybrid DNAs were cloned and propagated as virions in CV-1 monkey kidney cells by mixed infections at 41 degrees C with tsA58, an early mutant of SV40. The location, size, and orientation of the inserted lambda DNA segment was verified by restriction endonuclease digestions and by heteroduplex analysis. Clones with each of the two possible orientations of the lambda DNA segment were isolated. CV-1 cells infected with lambda-SV40 hybrid virus contain little or no lambda-specific RNA or proteins, even though the hybrid virus replicates nearly as well as the helper virus.

Cell Line↗
PubMed1976

Isolation and propagation of a segment of the simian virus 40 genome containing the origin of DNA replication.

Heteroduplex DNA molecules formed from two DNAs that differ from each other by a deletion can be cleaved at the mismatched region (a deletion loop) with the single-strand-specific S1 endonuclease. A heteroduplex DNA molecule, constructed from the DNA of simian virus 40 (SV40) mutant with a deletion of the map region 0.54-0.55 and the DNA of a second SV40 mutant having a deletion of the map segment 0.70-0.73, is cleaved twice with S1 endonuclease. One of the products is a DNA fragment of about 0.13 the length of SV40 DNA which contains the origin of SV40 DNA replication (0.67 on the SV40 DNA map).

DNA Replication↗
PubMed1976

Electron microscopy of gene regulation: the L-arabinose operon.

Unlike normal cells, malignant rat and two simian virus 40-transformed human cell lines can neither grow nor survive in B12- and folate-supplemented media in which methionine is replaced by homocysteine. Yet three lines of evidence indicate that the malignant and transformed cells synthesize large amounts of methionine endogenously through the reaction catalyzed by 5-methyltetrahydropterolyl-L-glutamate: L-homocysteine S-methyltransferase (EC 2.1.1.13). (1) The activities of this methyltransferase were comparable in extracts of malignant and normal cells. (2) The uptake of radioactive label from [5-14C]methyltetrahydropteroyl-L-glutamic acid (5-Me-H4PteGlu) was at least as great in the malignant cells as in the normals and was nearly totally dependent on the addition of homocysteine, the methyl acceptor; furthermore, 59-84% of the label incorporated by cells was recovered as methionine.

Arabinose↗
PubMed1976

Construction and analysis of viable deletion mutants of simian virus 40.

Viable mutants of simian virus 40 (SV40), with deletions ranging in size from 15 to 200 base pairs, have been obtained by infecting CV-1P cells with circularly permuted linear SV40 DNA. The linear DNA was produced by cleavage of closed circular DNA with DNase I in the presence of Mn2+, followed, in some cases, by mild digestion with lambda 5'-exonuclease. The SV40 map location and the size of each deletion were determined by using the S1 nuclease mapping procedure (Shenk et al., 1975) and the change in size of fragments produced by Hind II + III endonuclease cleavage. Deletions in at least three regions of the SV40 chromosome have slight or no effect on the rate or yield of viral multiplication and on vira-induced cellular transformation. These regions are located at the following coordinates on the SV40 physical map: 0.17 to 0.18; 0.54 to 0.59; and 0.68 to 0.74.

Cell Line↗
PubMed1976

Simian virus 40-permissive cell interactions: selection and characterization of spontaneously arising monkey cells that are resistant to simian virus 40 infection.

A fraction of permissive cells survive simian virus 40 (SV40) infection. The frequency of such surviving cells depends only upon the concentration of infecting virus, both parental and progeny, to which the cells are exposed during the course of selection. Surviving clones, which can be freed of virus by cloning in the presence of SV40 antiserum, are indistinguishable from parental cells in their growth of characteristics and display no SV40 antigen; thus they are not transformed. Most surviving clones are less than 10% as susceptible as parental cells to SV40 infection; 5 to 10% are less than 1% as susceptible. None of these SV40-resistant clones is absolutely resistant to SV40 infection. Analysis of 16 independently arising resistant clones indicates that they all block SV40 infection at an early stage after adsorption and eclipse but before full uncoating. Viral mutants have been isolated that partially overcome the block to infection in these cells; these host range viruses plaque on resistant lines fivefold more efficiently than wild-type SV40 and have a characteristic plaque morphology. Fluctuation analysis indicates that resistant cells arise spontaneously during the growth of normally susceptible permissive cells. Thus, SV40-resistant cells are selected for, not induced by, SV40 infection.

Adsorption↗
PubMed1975

Synthesis of Superhelical Simian Virus 40 Deoxyribonucleic Acid in Cell Lysates*.

In vivo-labeled SV40 replicating DNA molecules can be converted into covalently closed superhelical SV40 DNA (SV40(I) using a lysate of sv40-infected monkey cells containing intact nuclei. Replication in vitro occurred at one-third the in vivo rate for 30 min at 30 degrees. After 1 hour of incubation, about 54% of the replicating molecules had been converted to SV40(I), 5% to nicked, circular molecules (SV40(II), 5% to covalently closed dimers; the remainder failed to complete replication although 75% of the prelabeled daughter strands had been elongated to one-genome length. Density labeling in vitro showed that all replicating molecules had participated during DNA synthesis in vitro. Velocity and equilibrium sedimentation analysis of pulse-chased and labeled DNA using radioactive and density labels suggested that SV40 DNA synthesis in vitro was a continuation of normal ongoing DNA synthesis. Initiation of new rounds of SV40 DNA replication was not detectable.

Ammonium Sulfate↗
PubMed1975

Requirement of a Cytoplasmic Fraction for Synthesis of SV40 Deoxyribonucleic Acid in Isolated Nuclei*.

About 50% of the SV40 DNA in the process of replication (sv40(ri) dna) completed replication in lysates of infected BSC-1 cells by conversion to covalently closed, superhelical SV40 DNA (SV40(I) DNA). Fractionation of the lysate into nuclear and cytoplasmic components blocked 99% of the synthesis of SV40(I) DNA in the purified nuclei. The reconstituted system, made by adding back the cytoplasmic fraction before incubation at 30 degrees, completely restored the in vitro level of SV40(I) DNA synthesis. Preliminary characterization of the activity found in the cytoplasmic fraction suggested it was a soluble, heat-labile protein (or proteins) with a minimum molecular weight of about 30,000 and an active sulfhydryl group. The activity was present in both infected and uninfected monkey cells, and at a lower level in mouse, hamster, and human cell lines. Neither serum starvation nor cycloheximide treatment of cells diminished the activity in the cytoplasmic fraction. Purified cytoplasmic DNA polymerase from KB cells did not substitute for the cytoplasmic fraction which was required for elongation of newly synthesized DNA strands. In the absence of the cytoplasmic fraction, conversion of 4 S DNA into longer strands was inhibited, and SV40(RI) DNA appeared to be broken specifically at the replication forks.

Animals↗
PubMed1975

Biochemical method for mapping mutational alterations in DNA with S1 nuclease: the location of deletions and temperature-sensitive mutations in simian virus 40.

S1 nuclease (EC 3.1.4.X), a single-strand-specific nuclease, can be used to accurately map the location of mutational alterations in simian virus 40 (SV40) DNA. Deletions of between 32 and 190 base pairs, which are at or below the limit of detectability by conventional electron microscopic analysis of heteroduplex DNAs, have been located in this way. To map a deletion, a mixture of unit length, linear DNA, prepared from the SV40 deletion mutant and its wild-type parent, are denatured and reannealed to form heteroduplexes. S1 nuclease can cut such heteroduplexes at the nonbase-paired region to produce fragments whose lengths correspond to the position of the deletion. Similarly, specific fragments are produced when S1 nuclease cleaves a heteroduplex formed from the DNAs of SV40 temperature-sensitive mutants and either their revertants or wild-type parents. Thus, the positions of the nonhomology between these DNAs can be determined.

Aspergillus↗
PubMed1975

Biochemical procedure for production of small deletions in simian virus 40 DNA.

A simple biochemical procedure for producing small deletions (15 to 50 base pairs) at virtually any location in simian virus 40 DNA has been developed. The steps involved are: cleavage of the closed-circular DNA to produce a linear structure followed by 5'-exonuclease digestion to expose a short single-stranded segment at each 3' end of the molecule. Mutants containing deletions at the site of the cleavage are obtained by infecting permissive monkey kidney cells with the exonuclease-treated DNA in the presence or absence of a helper DNA (depending upon whether or not the site of cleavage and therefore the deletion occurred in a gene required for vegetative multiplication). In this paper viable mutants with deletions at the HpaII endonuclease cleavage site (0.735 map position) and defective trans-complementable mutants with deletions at the EcoRI endonuclease cleavage site (0/1.0 map position) were isolated.

Coliphages↗
PubMed1975

Electron microscope localization of a protein bound near the origin of simian virus 40 DNA replication.

A salt-stable complex of protein and viral DNA obtained from Simian virus 40 (SV40)-infected monkey cells or mature SV40 virions has a novel structure. When viewed by high resolution electron microscopy, the circular SV40 DNA molecule has bound to it one to three globular protein "knobs". Using ecoRI and hpaII restriction endonucleases, each of which can cleave SV40 DNA once at a known location (10, 11, 12, 14), the bound protein can be localized at 0.7 plus or minis 0.05 on the SV40 DNA physical map (SV40 fractional length, clockwise from the ecoRI endonuclease-cleavage site).

Animals↗