Levels of Rat Cellular RNA Homologous to Either Kirsten Sarcoma Virus or Rat Type-C Virus in Cell Lines Derived from Osborne-Mendel Rats

Abstract

DNA transcripts from V-NRK and RT21c rat type-C viruses were found to differ in their sequence homology to Kirsten and Harvey sarcoma viruses. V-NRK DNA transcripts consistently had homology to Kirsten and Harvey sarcoma virus, whereas RT21c DNA transcripts did not. To explain the differences, the nucleic acids and structural proteins of the two type-C viruses, released from each of two cell lines derived from Osborne-Mendel rats, were analyzed by molecular hybridization and competition radioimmunoassays. The p30 and p12 structural proteins of the two viruses were found to be highly related immunologically. In the V-NRK virus preparation, two sets of distinct RNA sequences were found in approximately equal amounts. One set is homologous to Ki-SV, and the other homologous to RT21c. In contrast, the RT21c virus preparation was found to contain a different ratio of these sequences. In this case the RT21c-like RNA sequences are present in 100-fold excess as compared to the additional Ki-SV specific sequences. Both NRK and RT21c cells contain in their DNA the full complement of Ki-SV homologous sequences, but NRK cells express much higher levels of these Ki-SV sequences in their RNA. These additional sequences, not homologous to RT21c, which are detected in uninfected NRK cellular RNA or V-NRK rat virus, could also be detected in the 60-70S RNA from a Moloney mouse type-C virus released from the NRK cells infected with the Moloney type-C virus. The results suggest that type-C viruses released from NRK cells incorporate species of RNA present in NRK cells which are homologous to Kirsten and Harvey sarcoma viruses. Either these sequences are of cellular origin, or rat cells contain two endogenous viruses with completely distinct nucleic acid sequences.

Two major sequence classes of ribosomal RNA genes inPlasmodium berghei

“…Alternatively unit C and unit A may not have a common progenitor and one gene may have integrated into the Plasmodium genome from a mitochondrial, host or viral source. Mitochondrial and viral DNA segments are commonly found in genomic DNA (13,14,15). The similarities among the four units, however, argues against this.…”

Defective retrovirus-like 30S RNA species of rat and mouse cells are infectious if packaged by type C helper virus

“…Earlier reports have described properties of the endogenous rat genetic information homologous to the rat-derived genes found in Ki-MSV and Ha-MSV (1, 6,15,17,20,27). The endogenous rat information is present in multiple copies in the DNA of uninfected rat species.…”

Endogenous mink (Mustela vison) type C virus isolated from sarcoma virus-transformed mink cells

“…The presence of mink viral RNA sequences in the extracellular virions released from transformed mink cells infected with type C viruses appears to differ from the pseudotyping of viral RNA that occurs in rescue experiments. For example, rat cells transcribe a subset of viral RNA sequences that appear in extracellular virions after rescue by different type C viruses (39,40,42). These sequences have contributed to the formation of sarcoma viral genomes after recombination with murine leukemia viruses (38).…”

“…Nonrepetitive cellular DNA was isolated by removing the highly reiterated DNA sequences that anneal by a Cot of 200 (40% of the total DNA) by fractionation on hydroxyapatite (8). DNA-DNA hybridizations were performed at 65°C in reaction mixtures containing 0.01 M Tris, pH 7.4, 0.75 M NaCl, 2 x 10-3 M EDTA, 0.05% sodium dodecyl sulfate, 40,000 cpm of 3H-labeled nonrepetitive DNA (0.2 jig) per ml, and 2 to 4 mg of cellular DNA per ml (8). The percentage hybrid is the saturating noalized value obtained after digestion of the hybrids with *the singlestrand-specific nuclease, S1 (1, 4).…”

“…The epithelioid morphology and high degree of contact inhibition exhibited by these cells has facilitated their use in assays for transformation by type C sarcoma viruses (20, 33) and in the isolation of a new class of focus-forming murine leukemia viruses (19). Nonproducer clones, derived from MvlLu celLs transformed by murine and feline sarcoma viruses, have been used to construct viral pseudotypes containing sarcoma viral genomes (20,32,33) and to develop sar-coma virus-specific DNA transcripts (38)(39)(40). Morphologically flat revertants selected from clones of nonproductively transformed cells have proven useful in assays for the enumeration of infectious, nontransforming leukemia viruses (32).…”