Two active forms of RD-114 virus DNA polymerase in infected cells.

Two forms of DNA polymerase are present in RD-114-infected human, dog, and mink cells, but are not detectable in uninfected cells. The two enzymes are indistinguishable catalytically and immunologically, but differ with respect to molecular weight and elution position from (dT)12-18-cellulose and phosphocellulose. The large enzyme (equivalent 95,000 daltons) is found in the infected cells, but not the virions produced by these cells. The virions contain only the smaller enzyme (equivalent 70,000 daltons). The larger form may represent a mammalian viral equivalent to the beta subunit of avian RNA tumor virus DNA polymerase.     

Endogenous RD-114 virus genome expression in malignant tissues of domestic cats.

Endogenous xenotropic cat type C virus (RD-114)- and infectious feline leukemia virus (FeLV)-specific gene expressions were measured in spontaneous sarcomas carcinomas, and nonmalignant cat tissues by molecular hybridization for virus-specific RNA and competition radio-immunoassays for the major internal protein (p30) of these two viruses. The results indicate that RD-114 gene expression in sarcomas and carcinomas at both RNA and p30 levels is significantly higher than histologically normal tissues from cats free of cancer. In contrast, the levels of FeLV viral RNA and p30 are fount to be low or undetectable in the majority of these tumored and normal tissues examined. Whereas variability in the amounts of RD-114 OR FeLV RNA and p30 expressed is found in tissues from different cats, their expression is fairly uniform in multiple malignant tissues of the same cat. The finding of widespread occurrence of elevated RD-114 gene expression in sarcomas and carcinomas is consistent with our similar observation with natural lymphomas of domestic cats and suggests that expression of certain functions of this endogenous virus may be etiologically involved in the development of many different spontaneous neoplasms of cats.     

Viral-specific antigen synthesis following de novo RD-114 virus infection of stationary cells

The cell cycle dependence of retrovirus replication was studied. Canine sarcoma (D-17) cells were infected de novo with the xenotropic feline retrovirus RD-114 under conditions previously reported to simultaneously inhibit virus replication and cell DNA synthesis and/or cell division. RD-114 viral antigen synthesis was observed under conditions previously reported to be inhibitory to avian and murine oncornavirus replication, including confluency and serum deprivation, X-irradiation, mitomycin C pretreatment, colchicine, and ethidium bromide treatments of cells. Several mechanisms that could account for viral antigen synthesis under the restrictive conditions used are discussed.     

Experimental infection of dogs with a feline endogenous retrovirus RD-114

Background  

The feline endogenous retrovirus RD114 is contained in the genome of cats. The virus may contaminate live canine vaccines based on cultured feline cells. The in vivo infectivity, acute and subacute pathogenicity, and viral proliferation of the RD114 virus were evaluated by experimental infection of dogs.     

Translation of duck hepatitis B virus reverse transcriptase by ribosomal shunting

The duck hepatitis B virus (DHBV) polymerase (P) is translated by de novo initiation from a downstream open reading frame (ORF) that partially overlaps the core (C) ORF on the bicistronic pregenomic RNA (pgRNA). The DHBV P AUG is in a poor context for translational initiation and is preceded by 14 AUGs that could intercept scanning ribosomes, yet P translation is unanticipatedly rapid. Therefore, we assessed C and P translation in the context of the pgRNA. Mutating the upstream C ORF revealed that P translation was inversely related to C translation, primarily due to occlusion of P translation by ribosomes translating C. Translation of the pgRNA was found to be cap dependent, because inserting a stem-loop (BamHI-SL) that blocked >90% of scanning ribosomes at the 5' end of the pgRNA greatly inhibited C and P synthesis. Neither mutating AUGs between the C and P start sites in contexts similar to that of the P AUG nor blocking ribosomal scanning by inserting the BamHI-SL between the C and P start codons greatly altered P translation, indicating that most ribosomes that translate P do not scan through these sequences. Finally, optimizing the P AUG context did not increase P translation. Therefore, the majority of the ribosomes that translate P are shunted from a donor region near the 5' end of the pgRNA to an acceptor site at or near the P AUG, and the shunt acceptor sequences may augment initiation at the P AUG.     

Isolation of an RD-114-Like Oncornavirus from a Cat Cell Line

A clone of cells derived from a continuous line of cat cells (CCC) spontaneously produced an RNA C-type virus (CCC virus) which did not have the group-specific antigen of the standard strains of feline leukemia viruses but did have that of the RD-114 virus. Single-hit infection of a virus yielding CCC cell with only the feline leukemia virus pseudotype of murine sarcoma virus [MSV(FeLV)] resulted in the release of a pseudotype of MSV coated with the CCC virus envelope. Host range, transmission of virus, helper functions, interference properties, and specific neutralization showed that the CCC and the RD-114 isolates as well as their respective MSV pseudotypes are closely similar if not identical. Parental, virus-negative cells frozen before the existence of RD-114 were chemically induced to yield CCC-like virus de novo. Infection of susceptible human cells with the chemically induced virus resulted in interference with the CCC virus pseudotype of MSV but not with the FeLV pseudotype of MSV.