Letter: Evidence for non-repetitive subunits in the genome of Rous sarcoma virus

Efficeint transcription of RNA into DNA by avian sarcoma virus polymerase

The DNAase digestion end-product of calf thymus DNA contains oligonucleotides that will function as primers for the efficient transcription into DNA of many naturally-occurring RNA's by purified avian sarcoma virus RNA-directed DNA polymerase. The labeled DNA transcripts so obtained are valuable as probes for molecular hybridization studies. Typical applications of the method include the efficient transcription into DNA of 18 and 28 S rRNA as well as the RNA's of avian sarcoma virus, polio virus, influenza virus, satellite tobacco necrosis virus and tobacco mosaic virus. In addition, when these primers are added to avian sarcoma virus particles that have been partially-disrupted with non-ionic detergent there is 6-fold stimulation of the endogenous RNA-directed DNA synthesis.

Endogenous oncornaviral DNA sequences: evidence for two classes of viral DNA sequences in guinea pig cells

The nature of the endogenous viral DNA sequences in guinea pig cells was studied by hybridization. A segment of the viral RNA (r-VRNA) hybridizing to abundant (or reiterated) DNA sequences (R-VDNA) was isolated by recycling to a Cot of 300. The hybridization of the recycled VRNA, as well as the total VRNA, was followed by determining their kinetics and by Wetmur-Davidson analysis. The kinetics of hybridization of total VRNA were complex, did not follow a second-order kinetics, and revealed two slopes by Wetmur-Davidson analysis. The recycled RNA, on the other hand, had a second-order reaction rate expected of the hybridization between a single species of RNA and DNA sequences and yielded a single straight line in a Wetmur-Davidson plot. The Cot1/2 and slope of the recycled r-VRNA was almost identical to that of the abundant VDNA sequences obtained from the hybridization data of the total VRNA. Guinea pig 28S rRNA with or without recycling was used in monitoring hybridization rate. The kinetics of hybridization of 28S RNA followed a second-order reaction and produced a single straight line by Wetmur-Davidson plot, with a second-order reassociation rate constant of 9.6 x 10(-3) liters/mol-s, a Cot1/2 of 104 mol-s/liter, and reiteration frequency of 146. There was no difference in the kinetics of hybridization of 28S RNA before and after recycling. These experiments showed that guinea pig cells contain two classes of VDNA sequences. (i) R-VDNA sequences with a second-order reassociation rate constant of 8.2 x 10(-4) liters/mol-s, a Cot1/2 of 1,219 mol-s/liter, and a reiteration frequency of 12 represent 37.5% of the viral genome. (ii) Unique VDNA sequences with a second-order reassociation rate constant of 1.2 x 10(-4) liters/mol-s, a Cot1/2 of 7,692 mol-s/liter, and a reiteration frequency of 2 represent 62.5% of the viral genome.

Analysis of the complexity and diversity of mRNA from chicken liver and oviduct

We have analyzed the sequence complexity and diversity of poly(A)-containing mRNA derived from two highly differentiated chicken tissues. Two independent approaches were used in our analyses. The first involves the annealing of cDNA copies of mRNA to a vast excess of the template RNA; the second procedure uses hybridization between highly radioactive single-copy genomic DNA and mRNA. The results obtained using these two experimental approaches are in good accord and reveal the presence of 12,000-15,000 diverse mRNA species in both chicken liver and oviduct. In both cell types, the kinetics of annealing of cDNA to its template mRNA demonstrate discrete frequency classes with most of the different mRNA species present in fewer than 10 copies per cell. 70% of oviduct mRNA, however, consists of about 10 abundant RNA species, which probably are responsible for the synthesis of the egg white proteins. The diversity of mRNA species in chicken liver and oviduct was further studied by heterologous annealing reactions between cDNA or singlecopy genomic DNA and a vast excess of mRNA. These studies demonstrate that 85% of the different mRNA sequences detected are present in both liver and oviduct, and suggest that the vast majority of the information expressed as mRNA is required for the maintenance of cellular functions common to all tissues.

Temperature-sensitive mutants of murine leukemia virus. IV. Further physiological characterization and evidence for genetic recombination

Several temperature-sensitive mutants of the Rauscher strain of murine leukemia virus representing three distinct physiological groups have been further characterized. Genetic recombination between different pairs of these mutants has been demonstrated. Several representative genetic recombinants were isolated and shown to replicate equally well at the permissive (31 C) and nonpermissive (38 C) temperatures and to have serological characteristics of the wild-type parental virus. Alternative models for the mechanisms involved in recombination between type C RNA viruses are discussed.

Evidence for crossing-over between avian tumor viruses based on analysis of viral RNAs

The RNAs of several avian tumor virus recombinants that had inherited their focus-forming ability from a sarcoma virus and their host range marker from a leukosis virus were investigated. Electrophoretic analyses showed that the cloned sarcoma virus recombinants contained only size class a RNA, although they had acquired a marker that resided on class b RNA in the leukosis virus parent. Class a RNA of different recombinant clones, derived from the same pair of parental viruses and selected for the same biological markers, differed slightly in electrophoretic mobility from each other and from the parental sarcoma virus. They were also found to have different fingerprints of RNase T1-resistant oligonucleotides. The average complexity of the 60-70S RNA prepared from Prague Rous sarcoma virus of subgroup B was estimated to be 3.5 x 10(6) daltons from the size of 20 RNase T1-resistant oligonucleotides, which represented 3.9% of the RNA and that of a recombinant to be 3.3 x 10(6) daltons from 23 oligonucleotides, which represented 4.7% of the RNA. This result suggests that the genome of wild-type and of recombinant RNA tumor viruses is polyploid. The sum of these observations led us to propose that recombination among avian tumor viruses occurred by crossing-over between homologous pieces of nucleic acid.

The nucleotide sequence complexity of avian tumor virus RNA

The nucleotide sequence complexity of 60-70S RNA of Rous sarcoma virus was determined from the molar yields of 11 pure oligonucleotides of known chain length, obtained from [(32)P]RNA of Rous sarcoma virus by T1 RNase digestion and two-dimensional polyacrylamide gel electrophoresis. We calculate an apparent chain length of about 9800 nucleotides, corresponding to a molecular weight of 3.4 x 10(6). Assuming the molecular weight of 60-70S RNA of Rous sarcoma virus to be about 10(7), our data suggest that the virus genome consists of identical, or very similar, nucleotide sequences repeated three to four times.

Measurement of the sequence complexity of cloned Moloney murine leukemia virus 60 to 70S RNA: evidence for a haploid genome

The sequence complexity of the 60-70S RNA complex from Moloney murine leukemia virus (M-MuLV) was determined by measuring the annealing rate of radioactively labeled virus-specific DNA with M-MuLV 60-70S RNA in conditions of vast RNA excess. The M-MuLV RNA annealing rate, characterized by the quantity C(r)t((1/2)), was compared with the C(r)t((1/2)) values for annealing of poliovirus 35S RNA (2.6 x 10(6) molecular weight) with poliovirus-specific DNA and Sindbis virus 42S RNA (4.3 x 10(6) molecular weight) with Sindbis-specific DNA. M-MuLV-specific DNA was prepared in vitro by the endogenous DNA polymerase reaction of M-MuLV virions, and poliovirus and Sindbis virus DNAs were prepared by incubation of viral RNA and DNA polymerase purified from avian myeloblastosis virus and an oligo deoxynucleotide primer. The poliovirus and Sindbis virus DNAs were sedimented through alkaline sucrose gradients, and those portions of the DNA with sizes similar to the M-MuLV DNA were selected out for the annealing measurements. M-MuLV was cloned on NIH-3T3 cells because it appeared possible that the standard source of M-MuLV for these experiments was a mixture of viruses. The annealing measurements indicated a sequence complexity of approximately 9 x 10(6) daltons for the cloned M-MuLV 60-70S RNA when standardized to poliovirus and Sindbis virus RNAs. This value supports the hypothesis that each of the 35S RNA subunits of M-MuLV 60-70S RNA has a different base sequence.