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Uptake of 3H-thymidine and its incorporation into DNA was studied in fibroblastic cell lines derived from normal individuals, patients with Fanconi anemia, and those heterozygous for this genetic trait. Uptake and incorporation for the normal cells were about five and seven times higher, respectively, than for Fanconi anemia fibroblasts; mean values for heterozygotes were intermediate. This effect was dependent on the duration of cell exposure to 3H-thymidine and was not observed with other labeled compounds. Thus, a genetically-determined metabolic defect may exist in Fanconi anemia patients which can be readily studied at the cellular level. This finding may be relevant to the observed clinical, cytogenetic, biochemical, and biologic properties related to expression of the Fanconi anemia gene.

3H-labeled 35S RNA from avian myeloblastosis virus (AMV), Rous associated virus (RAV)-0, RAV-60, RAV-61, RAV-2, or B-77(w) was hybridized with an excess of cellular DNA from different avian species, i.e., normal or leukemic chickens, normal pheasants, turkeys, Japanese quails, or ducks. Approximately two to three copies of endogenous viral DNA were estimated to be present per diploid of normal chicken cell genome. In leukemic chicken myeloblasts induced by AMV, the number of viral sequences appeared to have doubled. The hybrids formed between viral RNA and DNA from leukemic chicken cells melted with a Tm 1 to 6 C higher than that of hybrids formed between viral RNA and normal chicken cell DNA. All of the viral RNAs tested, except RAV-61, hybridized the most with DNA from AMV-infected chicken cells, followed by DNA from normal chicken cells, and then pheasant DNA. RAV-61 RNA hybridized maximally (39%) with pheasant DNA, followed by DNA from leukemic (34%), and then normal (29%) chicken cells. All viral RNAs tested hybridized little with Japanese quail DNA (2 to 5%), turkey DNA (2 to 4%), or duck DNA (1%). DNA from normal chicken cells contained only 60 to 70% of the RAV-60 genetic information, and normal pheasant cells lacked some RAV-61 DNA sequences. RAV-60 and RAV-61 genomes were more homologous to the RAV-0 genome than to the genome of RAV-2, AMV, or B-77(s). RAV-60 and RAV-61 appear to be recombinants between endogenous and exogenous viruses.

The distribution of oncornavirus DNA sequences in various tissues of normal chickens and of chickens with leukemia or kidney tumors induced by avian myeloblastosis virus (AMV) was analyzed by DNA-RNA hybridization using 35S AMV RNA as a probe. All the tissues from normal chickens which were tested contained the same average cellular concentration of endogenous oncornavirus DNA. In contrast, different tissues from lekemic chickens and from chickens bearing kidney tumors contained different concentrations of AMV homologous DNA: in some tissues there was no increase whereas other tissues acquired additional AMV-specific DNA sequences. The increase was the greatest in tissues which can become neoplastic after infection, such as myeloblasts, erythrocytes, and kidney cells. It was directly demonstrated that DNA from AMV-induced kidney tumor contains AMV sequences which are absent in DNA from normal cells. A similar finding had been previously obtained with leukemic cells (15). 3H-labeled 35S RNA from purified AMV was exhaustively hybridized with an excess of normal chicken DNA to remove all the viral RNA sequences which are complementary to DNA from uninfected cells. The 3H-labeled RNA which failed to hybridize was isolated by hydroxylapatite column chromatography which separates DNA-RNA hybrids from single-stranded RNA. The residual RNA hybridized to chicken kidney tumor DNA but did not rehybridize with normal chicken DNA.

Liquid hybridization of progressively smaller fragments (35S, 27S, 15.5S, 12.5S, and 8S) of poly(A)-selected avian myeloblastosis virus RNA with excess DNA from leukemic chicken myeloblasts revealed that all sizes of RNA contained sequences complementary to both slowly and rapidly hybridizing cellular DNA sequences. Apparently, the RNA sequences which hybridize rapidly with excesses of cellular DNA are not restricted to any one region of the avian myeloblastosis virus 35S RNA. Instead, they appear to be randomly distributed over the entire 35S avian myeloblastosis virus RNA molecule with some positioned within 200 nucleotides of the poly(A) tract at the 3' end of the RNA.

Oncostatin M is a polypeptide of Mr approximately 28,000 that acts as a growth regulator for many cultured mammalian cells. We report the cDNA and genomic cloning, sequence analysis, and functional expression in heterologous cells of oncostatin M. cDNA clones were isolated from mRNA of U937 cells that had been induced to differentiate into macrophagelike cells by treatment with phorbol 12-myristate 13-acetate, and a genomic clone was also isolated from human brain DNA. Sequence analysis of these clones established the 1,814-base-pair cDNA sequence as well as exon boundaries. This sequence predicted that oncostatin M is synthesized as a 252-amino-acid polypeptide, with a 25-residue hydrophobic sequence resembling a signal peptide at the N terminus. The predicted oncostatin M amino acid sequence shared no homology with other known proteins, but the sequence of the 3' noncoding region of the cDNA contained an A + T-rich stretch with sequence motifs found in the 3' untranslated regions of many cytokine and lymphokine cDNAs. Oncostatin M mRNA of approximately 2 kilobase pairs was detected in phorbol 12-myristate 13-acetate-treated U937 cells and in activated human T cells. Transfection of cDNA encoding the oncostatin M precursor into COS cells resulted in the secretion of proteins with the structural and functional properties of oncostatin M. The unique amino acid sequence, expression by lymphoid cells, and growth-regulatory activities of oncostatin M suggest that it is a novel cytokine.