Parvoviruses as contaminants of permanent human cell lines. V. The nucleic acid of KBSH-virus

KBSH parvovirus: comparison with porcine parvovirus

We compared the molecular, antigenic, and pathogenic properties of KBSH parvovirus to those of porcine parvovirus (PPV) isolate NADL-8. KBSH, propagated in swine testes cells in culture, possessed two major capsid polypeptides of 83 and 64 kilodaltons that were similar in size to those of PPV. KBSH-infected cells also contained an 86-kilodalton nonstructural polypeptide that was identical in size to the PPV nonstructural polypeptide (NS-1). The KBSH polypeptides were structurally similar but not identical to the corresponding PPV polypeptides, as revealed by partial proteolysis mapping. Viral replicative-form DNA from KBSH-infected cells was similar in size to PPV replicative-form DNA and exhibited similar but not identical restriction endonuclease cleavage patterns to that of PPV replicative-form DNA. Antigenically, the two viruses were also very closely related. By using heterologous and homologous antisera, the two viruses were indistinguishable in hemagglutination inhibition and immunoprecipitation assays. However, pathogenically these viruses were dramatically different. NADL-8 caused fetal death when injected into swine fetuses in utero and viremia and high persisting antibody titers when administered orally to weaning-age swine. KBSH-inoculated fetuses were normal in appearance, and pigs orally exposed to KBSH failed to establish viremia and demonstrated only transient antibody titers. Thus, KBSH appears to be a PPV that is very closely related to a highly pathogenic PPV isolate, yet is itself nonpathogenic in swine. This reduced pathogenic potential of KBSH may be attributable to its poor ability to replicate in swine.

Multiple buoyant densities of hepatitis A virus in cesium chloride gradients

Hepatitis A virus (HAV) recovered from stools of human cases of hepatitis A and from stools of chimpanzees experimentally infected with HAV was shown to possess multiple buoyant densities in CsCl gradients. The greatest proportion of HAV was most frequently found at a buoyant density of 1.32-1.34 g/cm3, however, large proportions of HAV were also frequently found at higher densities, including 1.36-1.37, 1.40-1.42, and 1.45-1.48 g/cm3. These findings are consistent with the notion that HAV may be a parvovirus.

Replication of the parvovirus MVM. II. Isolation and characterization of intermediates in the replication of the viral deoxyribonucleic acid

The time course of the appearance of intracellular viral DNA has been studied in mouse L cells infected with the single-stranded DNA virus MVM (minute virus of mice) by using a selective extraction procedure. Approximately half of this DNA elutes from hydroxyapatite as single-stranded DNA. It is sensitive to Escherichia coli exonuclease I and shows a sedimentation profile similar to DNA from the virus, suggesting that it is progeny viral DNA. The remainder of the selectively extracted DNA elutes from hydroxyapatite in the position of double-stranded DNA and is resistant to exonuclease I. Most of this DNA has a sedimentation coefficient of 14 to 16S, indicating that its molecular weight is twice that of the viral DNA. Denaturation renders the majority of the double-stranded DNA sensitive to exonuclease I, but a significant fraction renatures spontaneously in a monomolecular fashion, indicating that it has a cross-linked or hairpin structure. Chromatography of the double-stranded DNA on benzoylated diethylaminoethyl cellulose resolves two components, one with duplex structure and one which contains single-stranded regions. A short pulse label late in infection predominantly labels the latter class of DNA, suggesting that it contains replicating intermediates. The possible roles of these various forms of DNA in the replication of the viral genome are discussed.