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Biomedical subjects

P Berg

Publications and source records attributed to P Berg.

At least 271 records · Page 15Linked to original sources
PubMed1974

Viable deletion mutants of simian virus 40: selective isolation by means of a restriction endonuclease from Hemophilus parainfluenzae.

Resistance of simian virus 40 (SV40) DNA to cleavage by Hemophilus parainfluenzae II (HpaII) restriction endonuclease has been used as a positive, in vitro selection for mutants lacking the one HpaII endonuclease-cleavage site of wild-type SV40 DNA. Each of 10 viable mutants isolated by this procedure multiplies significantly more slowly than wild-type virus and contains a small deletion (80 to 190 base pairs in size) of the region of the genome that includes the HpaII endonuclease-recognition sequence. These well-defined mutants, having a selective disadvantage for growth, would not have been readily obtained by conventional methods used to screen for viral mutants. Therefore, in certain circumstances, restriction endonucleases are effective reagents for the selection of new classes of mutants. Because these small deletions can be visualized in heteroduplexes, these mutants provide internal markers for mapping other alterations or features of the simian virus 40 genome.

Animals↗
PubMed1973

Mapping of simian virus 40 early functions on the viral chromosome.

The simian virus 40 (SV40) DNA segment in the nondefective adenovirus 2-SV40 hybrid, Ad2(+)ND(4), is colinear with the segment between 0.11 and 0.59 SV40 fractional length from the site at which the R(1) restriction endonuclease cleaves SV40 DNA. This specifies the region of the SV40 DNA molecule which induces the early SV40 antigens: U antigen, tumor specific transplantation antigen, and T antigen. A variant of Ad2(+)ND(4), called Ad2(+)ND(4del), was found which has a deletion of the DNA segment between 0.50 and 0.57 SV40 fractional length from the R(1) endonuclease cleavage point.

Adenoviridae↗
PubMed1973

Cleavage of circular, superhelical simian virus 40 DNA to a linear duplex by S1 nuclease.

S(1) nuclease, the single-strand specific nuclease from Aspergillus oryzae can cleave both strands of circular covalently closed, superhelical simian virus 40 (SV40) DNA to generate unit length linear duplex molecules with intact single strands. But circular, covalently closed, nonsuperhelical DNA, as well as linear duplex molecules, are relatively resistant to attack by the enzyme. These findings indicate that unpaired or weakly hydrogen-bonded regions, sensitive to the single strand-specific nuclease, occur or can be induced in superhelical DNA. Nicked, circular SV40 DNA can be cleaved on the opposite strand at or near the nick to yield linear molecules. S(1) nuclease may be a useful reagent for cleaving DNAs at regions containing single-strand nicks. Unlike the restriction endonucleases, S(1) nuclease probably does not cleave SV40 DNA at a specific nucleotide sequence. Rather, the sites of cleavage occur within regions that are readily denaturable in a topologically constrained superhelical molecule. At moderate salt concentrations (75 mM) SV40 DNA is cleaved once, most often within either one of the two following regions: the segments defined as 0.15 to 0.25 and 0.45 to 0.55 SV40 fractional length, clockwise, from the EcoR(I) restriction endonuclease cleavage site (defined as the zero position on the SV40 DNA map). In higher salt (250 mM) cleavage occurs preferentially within the 0.45 to 0.55 segment of the map.

Aspergillus↗
PubMed1973

Location of the T4 gene 32 protein binding site on simian virus 40 DNA.

The T4 gene 32 protein, which binds to single-stranded but not duplex DNA, forms a specifically located denaturation loop in covalently closed circular simian virus 40 (SV40) DNA. Cleavage of the SV40 DNA-gene 32 protein complex with a restriction endonuclease from Hemophilus parainfluenzae shows the loop center to be at 0.46 on the SV40 DNA map. This is within one of the regions of SV40 DNA cleaved preferentially by the single-strand-specific nuclease S(1).

Binding Sites↗
PubMed1972

Biochemical method for inserting new genetic information into DNA of Simian Virus 40: circular SV40 DNA molecules containing lambda phage genes and the galactose operon of Escherichia coli.

We have developed methods for covalently joining duplex DNA molecules to one another and have used these techniques to construct circular dimers of SV40 DNA and to insert a DNA segment containing lambda phage genes and the galactose operon of E. coli into SV40 DNA. The method involves: (a) converting circular SV40 DNA to a linear form, (b) adding single-stranded homodeoxypolymeric extensions of defined composition and length to the 3' ends of one of the DNA strands with the enzyme terminal deoxynucleotidyl transferase (c) adding complementary homodeoxypolymeric extensions to the other DNA strand, (d) annealing the two DNA molecules to form a circular duplex structure, and (e) filling the gaps and sealing nicks in this structure with E. coli DNA polymerase and DNA ligase to form a covalently closed-circular DNA molecule.

Centrifugation, Density Gradient↗
PubMed1972

Cleavage of Simian virus 40 DNA at a unique site by a bacterial restriction enzyme.

The R(1) restriction endonuclease of Escherichia coli converts covalently-closed circular Simian Virus 40 (SV40) DNA to unit-length linear duplex molecules. Cleavage occurs at a unique site, since denaturation and renaturation of these linear molecules yield linear but no circular molecules. The distance from the cleavage site to the SV40 DNA sequence contained in the adenovirus-SV40 hybrid, Ad2(+)ND(1), is 0.11 of the length of SV40 DNA. T4 gene 32 protein binds to SV40 DNA in a region 0.45 of the length of SV40 DNA from the R(1) cleavage site. E. coli B restriction endonuclease can cleave SV40 DNA at several sites.

Adenoviridae↗