Nucleocapsid Protein Zinc-Finger Mutants of Simian Immunodeficiency Virus Strain Mne Produce Virions That Are Replication Defectivein Vitroandin Vivo

AbstractAll retroviruses (except the spumaretroviruses) contain a nucleocapsid (NC) protein that encodes one or two copies of the Zn2+-finger sequence -Cys-X2-Cys-X4-His-X4-Cys-. This region has been shown to be essential for recognition and packaging of the genomic RNA during virion particle assembly. Additionally, this region has been shown to be involved in early infection events in a wide spectrum of retroviruses, including mammalian type C [e.g., murine leukemia virus (MuLV)], human immunodeficiency virus type 1 (HIV-1),Rous sarcomavirus, and other retroviruses. Mutations in the two Zn2+-fingers of the NC protein of simian immunodeficiency virus strain Mne [SIV(Mne)] have been generated. The resulting virions contained the normal complement of processed viral proteins with densities indistinguishable from wild-type SIV(Mne). All of the mutants had electron micrograph morphologies similar to those of immature particles observed in wild-type preparations. RNA packaging was less affected by mutations in the NC protein of SIV(Mne) than has been observed for similar mutants in the MuLV and HIV-1 systems. Nevertheless,in vitroreplication of SIV(Mne) NC mutants was impaired to levels comparable to those observed for MuLV and HIV-1 NC mutants; replication defective NC mutants are typically 105- to 106-fold less infectious than similar levels of wild-type virus. One mutant, ΔCys33–Cys36, was also found to be noninfectiousin vivowhen mutant virus was administered intravenously to a pig-tailed macaque. NC mutations can therefore be used to generate replication defective virions for candidate vaccines in the SIV macaque model for primate lentiviral diseases

Partial Transcription of Murine Type C Viral Genomes in BALB/c Cell Lines

The mouse cell line, BALB/c 3T3, and its derivatives transformed either spontaneously or by treatment with a variety of external agents, were analyzed for cytoplasmic RNA complementary to DNA products prepared from the Kirsten strain of murine sarcoma-leukemia virus, and from an endogenous type C virus of BALB/c 3T3. Although none of these cell lines spontaneously releases complete type C virions, they all contain RNA which is partially homologous to a portion of the 35S RNA isolated from these viruses. The parental cell line, BALB/c 3T3, contains a low level of viral-related RNA, and there is an increased amount of this RNA in some of the transformed cells. The RNA detected represents only a fraction of the viral RNA found in virus-producing cells. The formation of RNA:DNA hybrids was detected by equilibrium centrifugation in Cs(2)SO(4) density gradients and by analysis with a single-strand-specific nuclease from Aspergillus oryzae. Viral DNA products prepared either from an endogenous reaction with whole virus in the presence of actinomycin D or from purified 70S viral RNA as template using avian myeloblastosis virus DNA polymerase yield comparable data. In addition, all of the BALB/c lines examined produce detectable levels of murine type C virus group-specific antigen

A Molecular Solution to the Riddle of the Giant Panda\u27s Phylogeny

Although it is generally agreed that the giant panda (Ailuropoda melanoleuca) is a member of the order Carn­vora, there has long been disagreement over whether it should be classified with bears, raccoons or as a single member of its own family. Four independent molecular and genetic measures lead to a consensus phylogeny for the giant and lesser pandas. The lesser panda diverged from New World procyonids at approximately the same time as their departure from ursids, while ancestors of the giant panda split from the ursid lineage much later, just before the radiation which led to modern bears. The giant panda\u27s divergence was accompanied by a chromosomal reorganization which can be partially reconstructed from the ursid karyotype, but not from that of procyonids or the lesser panda. The apparently dramatic, but actually limited, distinctions between the giant panda and the bears in chromosomal and anatomical morphology provide a graphic mammalian example of the discordance of molecular and morphological (and chromosomal) evolutionary change

Radioimmunoassay of mammalian type c viral proteins. Iii. Detection of viral antigen in normal murine cells and tissues.

A radioimmunoassay specific for a murine leukemia virus structural protein, the gs antigen, detects an antigenic reactivity in normal murine cells in culture and natural tissues. The assay was shown to measure an antigen that is highly related to the virion protein as shown by absorption tests, immunoadsorbent chromatography, and by analysis of linearized dose-response curves. These findings combined with the finding of viral-specific RNA indicate that portions of the viral genome are being expressed with a much greater frequency than previously appreciated