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Biomedical subjects

L Philipson

Publications and source records attributed to L Philipson.

At least 217 records · Page 12Linked to original sources
PubMed1971

Addition of polyadenylate sequences to virus-specific RNA during adenovirus replication.

Adenovirus-specific nuclear and polysomal RNA, both early and late in the infectious cycle, contain a covalently linked region of polyadenylic acid 150-250 nucleotides long. A large proportion of the adenovirus-specific messenger RNA contains poly(A). As revealed by hybridization experiments, the poly(A) is not transcribed from adenovirus DNA. Furthermore, an adenosine analogue, cordycepin, blocks the synthesis of poly(A) and also inhibits the accumulation of adenovirus messenger RNA on polysomes. Addition of poly(A) to viral RNA may involve a host-controlled mechanism that regulates the processing and transport of messenger RNA.

Acrylamides↗
PubMed1971

Protein A mutants of Staphylococcus aureus.

Staphylococcus aureus Cowan I was exposed to nitrosoguanidine or ethyl-methanesulfonate, and survivors were screened on nutrient agar plates containing rabbit anti-protein A serum for loss of protein A production. More than half of all protein A-deficient mutants also lacked nuclease, coagulase, alpha hemolysin, fibrinolysin, mannitol utilization, and the phage-type pattern. Mutants with a spectrum of these properties were also isolated. Induced or spontaneous reversions of the mutants were observed. The properties of the protein A-deficient mutants suggest that synthesis or release (or both) of a number of extracellular products of S. aureus is controlled by a common regulatory mechanism.

Acridines↗
PubMed1971

Specific alterations of coxsackievirus B3 eluted from HeLa cells.

After the attachment of radioactive coxsackievirus B3 to HeLa cells at 0 C and subsequent incubation at 37 C, 50 to 80% of attached virus radioactivity was eluted from the cells within 1 hr. Eluted virus had a buoyant density of 1.21 in a potassium tartrate gradient, sedimented more slowly than native virus in sucrose gradients, was resistant to ribonuclease, was unstable in CsCl centrifugation, and did not reattach to uninfected cells. Electrophoretic studies of sodium dodecyl sulfate-disrupted B3 virus in sodium dodecyl sulfate-polyacrylamide gels revealed four radioactive virus polypeptides (VP 1 to 4), of which the three largest migrated slightly faster than their poliovirus T1 counterparts. In contrast, electrophoretic analysis of eluted virus, after banding in a tartrate gradient or pelleting by centrifugation, showed the absence of the fastest migrating polypeptide, VP 4. VP 4 was recovered in the supernatant fluid when the eluted virions were removed by high-speed centrifugation. The results indicate that VP 4 is located at the surface of the native virion, and its dissociation from the capsid may represent the first specific alteration of the virion after virus-receptor interaction at the cell surface.

Amino Acids↗
PubMed1971

Mechanism of the arginine requirement for adenovirus synthesis. I. Synthesis of structural proteins.

The mechanism of the arginine requirement for adenovirus was studied in cultures of KB cells infected with adenovirus type 2. Macromolecular synthesis was found to be severely impaired in uninfected cells under complete arginine deprivation, whereas an arginine concentration of 50 mum yielded a moderate and reversible inhibition of growth and nucleic acid synthesis. At this concentration, viral structural proteins were accumulated in excess although the virus yield was reduced more than 1,000-fold. The arginine-sensitive step appeared to occur early during the first 15 hr postinfection in the virus growth cycle. Virus-infected cells deprived of arginine to 50 mum showed, when reversed, a 4- to 5-hr lag period before the increase in virus growth was observed. Analysis of the radioactive pattern of labeled virions synthesized after reversion showed that all polypeptides were synthesized after addition of arginine to the medium, and none of the virion-polypeptides which are revealed by gel electrophoresis appeared to be preferentially synthesized after arginine reversion. The excess pool of structural proteins formed during depletion appeared to a large extent to be unavailable for virus assembly.

Adenoviridae↗
PubMed1969

Early events of virus-cell interaction in an adenovirus system.

The interaction of (32)P-labeled adenovirus type 2 and HeLa or KB cells has been examined during early infection. The kinetics of virus uncoating to deoxyribonuclease-sensitive products, the partial characterization of three such products by gradient centrifugation, and the distribution of these products in the extranuclear and nuclear portions of infected cells are reported. The results are compatible with the following model. Extracellular virus attaches to a receptor on the plasma membrane. The membrane-bound virus has a half-life of less than 15 min and is transformed to a partly uncoated product which is free inside the cell and about half of which rapidly enters the cell nucleus. This is rapidly transformed, in both cytoplasm and nucleus, to a membrane-bound virion "core." The proteins of the bound "core" are then removed from the intact virus deoxyribonucleic acid (DNA). In the nucleus, viral DNA is the main product and there the overall sequence is completed in about 2 hr.

Adenoviridae↗
PubMed1968

Virus-receptor interaction in an adenovirus system.

HeLa or KB cells each contain around 10(4) receptor sites for adenovirus type 2. These are inactivated by treatment of live cells with subtilisin. The receptor activity of the enzyme-treated cells is regained after 4 to 8 hr of incubation in complete medium. A technique that utilizes the difference in buoyant density between free virus and virus-receptor complex was developed to demonstrate receptor activity. Cellular fractionation revealed that receptors were confined mainly to the plasma membrane fraction and that negligible receptor activity could be demonstrated in enzyme-treated cells. Subtilisin probably did not penetrate the cell membrane; thus, the receptors are limited to the cell surface. Purified fiber of the virion completely prevents attachment of adenovirus types 2 and 5 to receptor sites at a ratio of 10(5) protein molecules per cell. Adsorption studies indicate that 10(5) to 10(6) receptor sites are available for the structural protein. The fiber does not affect attachment of poliovirus type 1.

Adenoviridae↗