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At least 919 records · Page 51Linked to original sources
PubMed1985

Use of a focal immunofluorescence assay on live cells for quantitation of retroviruses: distinction of host range classes in virus mixtures and biological cloning of dual-tropic murine leukemia viruses.

A rapid and sensitive focal immunofluorescence assay (FIA) using monoclonal antibodies or heterologous antisera was employed for detection and biological cloning of viruses capable of inducing viral antigens on cell surfaces. The FIA was performed directly on a variety of live cells in tissue culture dishes and was used successfully with C-type murine leukemia viruses (MuLV) of different tropism including ecotropic, xenotropic, amphotropic, and dual-tropic recombinant mink cell focus-inducing (MCF) viruses. With the FIA, we were able to titrate and distinguish ecotropic Friend-MuLV and Friend-MCF viruses present in mixtures. Dual-tropic MCF viruses could be specifically detected directly in mouse cells by using MCF-specific monoclonal antibodies. These antibodies replaced the requirement for production of typical MCF cytopathic effect in mink cells for MCF virus detection, and also allowed efficient titration in mouse cells of MCF virions pseudotyped with ecotropic envelope proteins. Furthermore, by picking foci of fluorescent cells and using their cell-free viral progeny, MCF viruses were cloned from complex pseudotypic mixtures. This allowed the cloning of viruses present at low frequency in heterogeneous mixtures obtained from leukemic tissues.

Animals↗
PubMed1987

The attachment sites of T5-host range temperate coliphages.

The attachment sites of 13 temperate coliphages were determined. Specialized transduction of proAB mutants was shown by eight isolates and of a his mutant by another two. Two isolates were concluded to integrate at atthtt and the integration site of one isolate remained undetermined.

Base Sequence↗
PubMed1988

Host range mutants of adenovirus type 12 E1 defective for lytic infection, transformation, and oncogenicity.

The human adenovirus type 12 (H12) E1A region encodes two early proteins of 266 amino acid residues (266R) and 235R whilst the H12 E1B promoter directs the synthesis of two major proteins of 163R and 482R. To determine the functions of E1A and E1B in lytic infection and oncogenic transformation we have isolated and characterized a series of H12 E1 mutants. Mutant H12 hr 700 contains a point mutation in exon 1 that alters a single amino acid common to both the 266 and 235R proteins. This mutant synthesized reduced levels of E1 and structural proteins at delayed times in HEK cells, transformed BRK cells, and induced tumors in newborn rats at reduced efficiency compared to wild-type virus. The mutation in H12 in 600 truncates the 266R protein in its unique sequences but this mutant synthesized the 235R, E1B, and structural proteins at delayed times in HEK cells. H12 in 600 was nontransforming but induced rare tumors in newborn rats. A third E1A mutant H12 in 601 synthesized no E1A proteins, reduced levels of E1B and structural proteins at delayed times in lytic infections, and was not a transforming or oncogenic virus. Three E1B mutants were studied in detail. Both H12 hr 703 and H12 in 602 encode N-terminal truncated 482R proteins whereas H12 del 620 encodes an in-frame internally deleted 482R protein. All three synthesized reduced amounts of E1A proteins and the E1B 163R protein, identifying a regulatory function for the 482R protein. None of the E1B mutants could transform and only H12 del 620 could induce rare tumors in newborn rats. These results show that H12 oncogenesis requires the coordinated expression of the E1 proteins.

Adenovirus Early Proteins↗
PubMed1989

Separation of host range from transformation functions of the hr-t gene of polyomavirus.

hr-t mutants of polyomavirus are defective in virus growth as well as in cell transformation, and have genetic alterations that invariably affect both the middle and small T proteins. We have examined the growth properties of three site-directed mutants that either eliminate or alter the middle T without affecting the small T protein. Mutant 808A encodes large and small T proteins but no middle T; it grew poorly in NIH 3T3 cells. In contrast, mutants 1387T and 1178T which express altered middle T along with normal large and small T proteins grew nearly as well as wild-type virus. Thus, although the altered middle T proteins encoded by 1387T and 1178T are defective for cell transformation, they retained the ability to induce expression of a cellular permissivity factor(s) required for virus production. At the biochemical level, the induction of permissivity by middle T was manifested primarily in terms of phosphorylation of VP1 on threonine and in efficient encapsidation of viral DNA to form infectious virus. The natural role of middle T involves regulation of phosphorylation events, and can be enacted, at least in part, independently of interactions with pp60c-src.

Animals↗
PubMed1979

Isolation of adenovirus type 5 host range deletion mutants defective for transformation of rat embryo cells.

A series of adenovirus type 5 (Ad5) deletion, insertion and substitution mutants, some of which are defective for transformation of rat cells, have been isolated. The mutants were selected as variants which lack the Xba I endonuclease cleavage site at 4 map units on the viral chromosome. The deletions range in size from 150-2300 bp and are located between 1.5 and 10.5 map units. The mutants can be propagated in 293 cells (Ad5-transformed human embryonic kidney cells), but are defective for growth in HeLa or human embryonic kidney cells. No viral DNA synthesis was observed in mutant virus-infected HeLa cells. All but one of the deletion mutants tested were defective for transformation of rat embryo and rat embryo brain cells.

Adenoviridae↗