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Biomedical subjects

J A Leong

Publications and source records attributed to J A Leong.

7 recordsLinked to original sources
PubMed1992

Staphylococcal coagglutination, a rapid method of identifying infectious hematopoietic necrosis virus.

A staphylococcal coagglutination test was developed for the rapid detection of infectious hematopoietic necrosis virus (IHNV) in cell cultures and infected fish. The test could be completed in 15 min but required a minimum IHNV titer of 10(6) PFU/ml to obtain a positive reaction. All IHNV isolates, representing the five electropherotypes taken from a wide variety of species and different geographic ranges, caused coagglutination of Staphylococcus aureus cells sensitized with rabbit polyclonal serum against the Round Butte IHNV isolate. The coagglutination reaction was blocked by preincubation of IHNV with homologous antiserum, and IHNV did not cause coagglutination of S. aureus cells sensitized with normal rabbit serum. In specificity tests, cells sensitized with rabbit anti-IHNV serum or normal serum did not coagglutinate in the presence of infectious pancreatic necrosis virus, viral hemorrhagic septicemia virus, cell culture medium components, or media from cultures of cell lines of salmonid and nonsalmonid origin. Most importantly, the coagglutination test was able to detect and identify IHNV directly from experimentally infected rainbow trout fry, the organs of naturally infected adult kokanee salmon and winter steelhead trout, and ovarian fluids of the winter steelhead trout. The coagglutination test is very suitable for field use, since it is inexpensive, simple to interpret, sensitive, and rapid and requires no specialized equipment.

Agglutination Tests↗
PubMed1991

Sequence analysis of infectious pancreatic necrosis virus genome segment B and its encoded VP1 protein: a putative RNA-dependent RNA polymerase lacking the Gly-Asp-Asp motif.

The genome segment B sequence of infectious pancreatic necrosis virus was determined for both the Jasper and Sp serotypes. The sequences are 2784 and 2630 bp long, respectively, and contain a single large open reading frame encoding the VP1 protein, the putative RNA-dependent RNA polymerase (RdRp) of IPNV. The proteins exhibit an 88% homology with each other, but only 41% with infectious bursal disease virus (IBDV) VP1, another member of the Birnaviridae. Despite the low overall homology between the IPNV and IBDV VP1 proteins, homologous regions were detected within the central portion of the proteins. The carboxy-proximal regions of the VP1, which contain very low amino acid homology, displayed evidence of conservation in structural features such as a hydrophilic, highly basic domain. Consensus sequences associated with GTP-binding proteins and RdRps were also detected in VP1. However, unlike the RdRps associated with single-stranded plus RNA viruses, the birnavirus RdRp lacks the Gly-Asp-Asp motif characteristic of this enzyme family.

Amino Acid Sequence↗
PubMed1990

Expression of the glycoprotein gene from a fish rhabdovirus by using baculovirus vectors.

A cDNA fragment containing the gene encoding the glycoprotein of infectious hematopoietic necrosis virus was inserted into Autographa californica baculovirus vectors under the control of the polyhedrin promoter. A 66-kilodalton protein, identical in size to the glycosylated glycoprotein of infectious hematopoietic necrosis virus, was expressed at high levels in Spodoptera frugiperda cells infected with the recombinant viruses. The expressed protein reacted with antiserum to the glycoprotein on Western blots (immunoblots).

Animals↗
PubMed1978

Normal human placentas contain RNA-directed DNA polymerase activity like that in viruses.

Extracts from over 100 normal human placentas have been examined for RNA-directed DNA polymerase (DNA nucleotidyltransferase, EC 2.7.7.7) activity. More than 80% of these placentas contained this enzyme activity, which banded at a density of 1.15-1.17 g/ml in sucrose. After heat treatment, this enzyme activity was shifted in density to 1.22-1.24 g/ml. The enzymatic activity was greater with (rC)n.(dG)12-18 than with (dC)n.(dG)12-18 and was not stimulated by (dG)12-18 alone. The product of the endogenous reaction, which was sensitive to RNase, had the characteristics of a small DNA associated with a large RNA by hydrogen bonding. Electron microscopic inspection of the material with a density of 1.15-1.17 g/ml revealed numerous retrovirus-like particles with central electron-dense cores and double-membraned envelopes. The enzyme may be associated with the retrovirus-lik particles noted in the trophoblast layer of some human placentas.

Female↗
PubMed1976

Effect of passage in culture on a clone of BALB/c 3T3 cells transformed by simian virus 40.

Most simian virus 40 (SV40)-transformed BALB/c 3T3 clones employed for biochemical studies have been used without regard to passage level. To determine whether virus-induced properties are stable as a function of passage, we have extensively characterized one transformed clone, FNE, which was isolated after SV40 infection BALB/c 3T3 cells in factor-free medium. From the initial testing at passage 5 and for at least 50 subsequent subcultures, the cells stably maintained many transformed growth properties, including high saturation density, morphology, colony formation on contact-inhibited monolayers, tumorigenicity, and synthesis of viral-specific RNA. However, other properties varied as a function of passage. There was a slight decrease in viral genome equivalents per cell from 1.1 copy/cell at passage 5 to 0.7 copies at passage 40. Initially, the cells were negative for all type C virus; however, cells carried at low density for 13 to 20 passages (65 to 100 generations) began to release an endogenous type C virus that then persisted in the culture. Spontaneous release of type C virus did not occur in control BALB/c 3T3 cells carried under identical culture conditions for 90 passages. When the cultures were releasing type C viruses they stained uniformly and brightly positive for SV40 tumor (T) antigen by immunofluorescence, whereas T antigen staining was variable at early passage. These experiments suggest that subtle but perhaps important differences in viral gene expression can occur as a function of passage; they also demonstrate the importance of evaluating the interactions between SV40 and endogenous type C viruses.

Animals↗