The a subunit in the RNA of transforming avian tumor viruses. I. Occurrence in different virus strains. II. Spontaneous loss resulting in nontransforming variants

Properties and location of poly(A) in Rous sarcoma virus RNA

The poly(A) sequence of 30 to 40S Rous sarcoma virus RNA, prepared by digestion of the RNA with RNase T(1), showed a rather homogenous electrophoretic distribution in formamide-polyacrylamide gels. Its size was estimated to be about 200 AMP residues. The poly(A) appears to be located at or near the 3' end of the 30 to 40S RNA because: (i) it contained one adenosine per 180 AMP residues, and because (ii) incubation of 30 to 40S RNA with bacterial RNase H in the presence of poly(dT) removed its poly(A) without significantly affecting its hydrodynamic or electrophoretic properties in denaturing solvents. The viral 60 to 70S RNA complex was found to consist of 30 to 40S subunits both with (65%) and without (approximately 30%) poly(A). The heteropolymeric sequences of these two species of 30 to 40S subunits have the same RNase T(1)-resistant oligonucleotide composition. Some, perhaps all, RNase T(1)-resistant oligonucleotides of 30 to 40S Rous sarcoma virus RNA appear to have a unique location relative to the poly(A) sequence, because the complexity of poly(A)-tagged fragments of 30 to 40S RNA decreased with decreasing size of the fragment. Two RNase T(1)-resistant oligonucleotides which distinguish sarcoma virus Prague B RNA from that of a transformation-defective deletion mutant of the same virus appear to be associated with an 11S poly(A)-tagged fragment of Prague B RNA. Thus RNA sequences concerned with cell transformation seem to be located within 5 to 10% of the 3' terminus of Prague B RNA.

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.

Structure and molecular length of the large subunits of RD-114 viral RNA

By electron microscopy, the large subunits of RD-114 RNA have a molecular weight of 5.0 x 10(6); they all have a characteristic secondary structure feature close to the middle.

Proposal for numbering mutants of avian leukosis and sarcoma viruses

A system for the numbering of mutants of avian sarcoma and leukosis viruses is proposed.

Isolation of defective mutant of avian sarcoma virus

A colony of transformed cells was isolated from chick-embryo cells infected with a stock of nondefective Schmidt-Ruppin strain of Rous sarcoma virus. The virus recovered from this colony was a stable defective mutant very similar to the Bryan strain of Rous sarcoma virus in the following characteristics: (i) noninfectiousness of virus particles released from transformed cells that lack helper factor; (ii) formation of infectious pseudotypes by coinfection with avian leukosis virus or by interaction with endogenous-helper factor in chicken cells; (iii) ability of the noninfectious form of virus to transform chick-embryo cells in the presence of ultraviolet light-inactivated Sendai virus; (iv) absence of glycoprotein in the noninfectious form; (v) failure to produce nondefective virus by recombination with avian leukosis virus; and (vi) segregation of polymerase-negative virus. The morphology of transformed cells is characteristic of those infected by the Schmidt-Ruppin strain. The demonstration of segregation of such a defective virus from nondefective sarcoma virus and failure to detect revertants of this mutant suggest that the deletion of some genes may be involved in this mutation.

Gel electrophoresis of avian leukosis and sarcoma viral RNA in formamide: comparison with other viral and cellular RNA species

Class a and class b 30 to 40S RNA subunits obtained by heat dissociation from the 60 to 70S RNA complex of avian tumor viruses were compared with several RNA standards by electrophoresis in formamide-polyacrylamide gels. Class a RNA was found to have a lower electrophoretic mobility and hence probably a higher molecular weight than class b RNA. The absolute molecular weight of class a and b RNA could not be determined with accuracy, because the relationship between logarithm of molecular weight and mobility of the RNA standards was not linear. The size of class a RNA fell into the range of 2.4 x 10(6) to 3.4 x 10(6) daltons and that of class b into the range of 2.2 x 10(6) to 2.9 x 10(6) daltons, depending on the standards used. The possible biological significance of this difference is discussed.

Studies on the nucleic acid sequences of Kirsten sarcoma virus: a model for formation of a mammalian RNA-containing sarcoma virus

The genetic information contained in the Kirsten and Moloney strains of mammalian RNA-containing sarcoma viruses has been analyzed by RNA . (3)H-DNA hybridization. Kirsten sarcoma virus has been found to possess two distinct sets of nucleic acid sequences. One set of sequences is contained in murine type C helper virus, and the other set is contained in rat type C helper virus. Moloney sarcoma virus contains sequences of murine type C helper virus but not of rat type C helper virus. The results indicate that Kirsten sarcoma virus arose through a process of recombination between Kirsten murine leukemia virus and nucleic acid sequences found in rat cells. A model is suggested for the formation of transforming type C viruses involving the transduction of oncogenic information.

Avian tumor virus RNA: a comparison of three sarcoma viruses and their transformation-defective derivatives by oligonucleotide fingerprinting and DNA-RNA hybridization

Earlier electrophoretic analyses have shown that the 60-70S RNA of avian sarcoma viruses contains a characteristic subunit, termed class a subunit, which has a lower electrophoretic mobility than class b subunit found in transformation-defective derivatives of sarcoma viruses and in avian leukosis viruses. We have compared the RNAs of three nondefective avian sarcoma viruses, B77 and Prague and Schmidt-Ruppin strains of Rous sarcoma virus, with those of their transformation-defective (td) derivatives, td B77, td PR-C, and td SR-A, respectively, to determine the chemical basis for the difference between class a and b subunits. It was found by "fingerprinting" that (1) all (about 20-25) large T1 RNase-resistant oligonucleotides present in class b subunits of transformation-defective viruses have homologous counterparts in the class a subunits of corresponding nondefective sarcoma viruses and that (2) class a subunits contain a few (one or two) additional oligonucleotides that are not present in class b. By contrast the oligonucleotide fingerprints of avian tumor viruses of different strains and subgroups were very different.Cross hybridization of classes a and b RNA of sarcoma virus B77 with DNA transcribed from a corresponding transformation-defective virus td B77 showed that the two RNAs share at least 60% and differ by about 10% of their sequences. It is suggested that the structural relationship of class a and b subunits of corresponding viruses may be expressed as a = b + x, and that all the oligonucleotides present only in RNAs of sarcoma viruses but not in transformation-defective viruses of the corresponding strains are part of sequence(s) x. The possibility that x represents genetic information directly or indirectly involved in transformation of fibroblasts is discussed.

Structural rearrangement and subunit composition of RNA from released Soehner-Dmochowski murine sarcoma virions

Two types of genomic, high-molecular-weight RNA species were found in Soehner-Dmochowski murine sarcoma virions released from virus-induced rat tumor cells grown in tissue culture. The type of RNA species observed depended on the length of exposure of the tumor cells to radioactive precursor. Early RNA of virions labeled up to 4 h with radioactive uridine had a sedimentation coefficient of 50S, and late RNA of virions labeled for 24 h had a sedimentation coefficient of 58S. Thermal transitions of early and late RNA indicated a difference in the configuration or structure of these two types of RNA. The late RNA may represent either a different configurational state of the early RNA or an aggregate molecule of two early RNA components joined together. Heat dissociation revealed that the major subunit of both RNA types was a 28S species, which was not susceptible to degradation by the addition of micrococcal nuclease to virions. A transitional, intermediate RNA species with a sedimentation coefficient of 37 to 40S was detected when early RNA was dissociated by dimethyl sulfoxide or heat at temperatures suboptimal for complete conversion. No free RNA subunit components were detected in virions harvested at intervals as short as 30 s or 5 min. A model for the assembly of genomic RNA from 28S RNA subunits is proposed.