Structural studies on oncornavirus-related sequences in chicken genomic DNA: two-step analyses of EcoRI and Bgl I restriction digests and tentative mapping of a ubiquitous endogenous provirus digests and tentative mapping of a ubiquitous endogenous provirus.

Abstract

DNA from a variety of uninfected chicken cell types has been analyzed by using restriction endonuclease digestion and RPC-5 ion-exchange chromatography followed by agarose gel electrophoresis. Endogenous retrovirus sequences were detected by using a 32P-labeled avian leukosis viral RNA probe. One simple pattern was identified in an individual containing unexpressed endogenous proviral genes (gs-chf-phenotype for group-specific antigens and chicken helper factor) that was common to all individuals studied. A tentative restriction map has been derived for this and one other gs-chfendogenous provirus. Other gs-chf-individuals and individuals with other phenotypes (e.g., gs+ chf+ and gsL chfhE) showed more complicated patterns that often included additional bands and thus probably additional proviruses. RNA from an avian sarcoma virus was used to detect cellular sequences (sarc) homologous to the viral transforming gene (src). Results have revealed that a single restriction endonuclease EcoRI fragment of 13 X 106 daltons contains the majority of these sequences and confirm that they are not adjacent to the endogenous provirus.Uninfected chicken cells possess DNA sequences homologous to at least part of the RNA genomes of the avian retroviruses (1-5). Nucleic acid hybridization has shown these endogenous proviral sequences to be present in a few copies per haploid genome; however, a precise determination of the copy number is not possible by this technique (1, 4). Cells from certain chicken lines spontaneously release an endogenous virus, Rous-associated virus type 0 (RAV-0), (6, 7). These lines and other normally nonproducing lines that can be chemically induced to release virus (8, 9) must contain a complete viral genome that is capable of expression. In other lines, partial expression of the endogenous provirus results in production of viral core proteins [group-specific antigens (gs)] and envelope proteins [chicken helper factors (chf)] (10, 11). In addition to the gs-chf-phenotype, which does not produce either viral product, two other phenotypes have been described: gs+ chf+, in which both products are made (12, 13), and gsL chfhE in which gs antigens are produced at low levels and helper is produced at high levels (14, 15). By nucleic acid hybridization, the amount of viral specific DNA appears to be the same in all three phenotypes (1, 2, 16). However, Hayward and Hanafusa (17,18) have shown quantitative and qualitative differences in the virus-specific RNAs. Thus, differences in expression may be regulated at the transcriptional level.In addition to the endogenous provirus, all chicken cells contain DNA homologous to the transformation-specific (src) gene of avian sarcoma viruses (19). These cellular sequences (called "sarc") are not linked to the provirus (20) and are independently transcribed into poly(A)-RNA that is found in polysomes (21,22). The function of sarc in normal cells is ullknown.To investigate the organization of the provirus in normal cellular DNA and its possible relationship to vi...

Variety of Endogenous Proviruses in the Genomes of Chickens of Different Breeds

“…The interpretation of the results was mainly based on the known physical map of RAV-O genome (McClements et al, 1979). Peculiarities of endogenous proviruses of various breeds of chickens were evaluated by comparison with white leghorns since the latter breed have been extensively studied (Astrin, 1978;Astrin et al, 1979a, b;McClements et al, 1979;Hughes et al, 1979 b).…”

“…cDNAs of oncoviruses are often contaminated by ribosomal RNA sequences (McClements et al, 1979). This may lead to the artefacts (Sabran et al, 1979).…”

“…The very high level of homology of RAV-2 and RAV-O genomes (Shoyab & Baluda, 1976) and the simplicity of growing RAV-2 in culture are the reasons for using 3~p-labelled cDNA RAV-2 for the detection of endogenous virus sequences in chicken DNA. The possibility of using RAV-2 for the detection of RAV-O sequences has been carefully examined already (Astrin, 1978;McClements et al, 1979).…”

“…2) corresponding to the same endogenous provirus. This RAV-O-like endogenous virus locus, named ev-1 (Astrin, 1978), is the most widely spread in the genomes of white leghorns (Astrin, 1978;McClements et al, 1979;Hughes et al, 1979 b). Besides the bands of ev-1 provirus, there were some other bands on the autoradiograms of different individual samples of white leghorn DNA corresponding to the other, lesser frequent, endogenous provirus with a different localization.…”

“…The provirus in the locus named ev-1 is found in the overwhelming majority of white leghorns being probably the most ancient; the others have been found with various but lesser frequency (Astrin, 1978;Astrin et al, 1979b). Since the genomes of red junglefowls contained endogenous RAV-O-like sequences (Frisby et al, 1979) it seemed to be very probable that the facts obtained from study of hundreds of white leghorns (Astrin, 1978;McClements et al, 1979;Hughes et al, 1979a) would turn out to be true for all chickens. Using brown leghorn chickens in our studies, however, we have noticed a lot of differences between endogenous provirus sequences in DNA of these chickens and white leghorns.…”