Nucleotide sequence of the p21 transforming protein of Harvey murine sarcoma virus

Expression of ki-ras oncogene in tumor cell variants exhibiting different metastatic capabilities

The expression of oncogenes in well-characterized B16 melanoma and UV-2237 fibrosarcoma cell variants that exhibit distinct metastatic properties was explored. The search for the expression of 11 different oncogenes revealed that the major oncogene in those two tumor systems is the Kirsten-ras (ki-ras). The results indicate that the amounts of specific ki-ras mRNA and the p21 protein are similar in both low- and high-metastatic counterparts. These results suggest that in these systems there is no apparent direct correlation between the amount and expression of the major cellular oncogene so far identified and the metastatic potential of these tumor cells.

An appraisal of the application of recombinant DNA techniques to chromosome defects

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Characterization of functional domains of p21 ras by use of chimeric genes

Comparison of the predicted amino acid sequences of different members of the ras family in vertebrates has shown that the N-terminal 120 residues are highly conserved while the C terminus is variable. To test the possible role of the variable residues in cell transformation, chimeras were constructed containing the N-terminal 111 amino acids of the human Ha-ras EJ oncogene and the C terminus of two Drosophila ras genes. We show that one of these constructs which has only 20 conserved residues between positions 121 and 189, can transform rat-1 cells, and the transformed cells are capable of inducing lethal tumors in rats. The second construct containing the C terminus of another Drosophila ras gene exhibits a transforming capacity as well, but only after linkage to a viral transcriptional promoter. These results show that the majority of residues within the C terminus can be replaced without abolishing the transforming potential of p21 ras.

Analysis of viral and somatic activations of the cHa-ras gene

The activation of the cHa-ras oncogene in the EJ/T24 bladder carcinoma cell line was compared with the activation of the same gene in the rat-derived Harvey murine sarcoma virus. The results indicate that, like the human oncogene, the Harvey murine sarcoma virus-borne ras gene owes its oncogenic capacity to point mutations in coding sequences rather than to the alteration in transcriptional control that occurred when the formerly cellular ras sequences were acquired by the virus. The viral gene retained its transforming ability when its transcription was removed from the influence of the retroviral long terminal repeat promoter and was placed under the regulation of the cHa-ras promoter. Conversely, the viral long terminal repeat was insufficient to activate the normal cHa-ras allele when a single copy of such a construct was delivered to a cell by viral infection. In addition to their mode of activation, the biological properties of the EJ/T24 and Harvey murine sarcoma virus oncogenes were compared by infecting newborn mice with chimeric retroviruses bearing each form. The two alleles acted equivalently, causing erythroleukemias and sarcomas with similar kinetics.

Ha-ras proteins exhibit GTPase activity: point mutations that activate Ha-ras gene products result in decreased GTPase activity

Several ras genes have been expressed at high levels in Escherichia coli and the resultant ras proteins were shown to be functional with respect to their well-known specific, high-affinity, GDP/GTP binding. We were able to detect a weak GTPase activity associated with the purified proteins. The normal cellular ras protein (p21N) exhibits approximately equal to 10 times higher GTPase activity than the "activated" proteins. Even though the turnover rate of the reaction is very low (0.02 mol of GTP hydrolyzed per mol of p21N protein per minute), the reaction appears to be catalytic; one molecule of p21N hydrolyzes more than one molecule of GTP. The GTPase and the GDP binding activities both have been recovered from a Mr 23,000 protein eluted following NaDodSO4/polyacrylamide gel electrophoresis, suggesting that these two activities are associated with the same protein. Mg2+ ions and dithiothreitol are required for GTPase activity and the optimal pH is between 7 and 8. Guanidine X HCl, which is required for solubilizing bacterially expressed ras protein, is strongly inhibitory to GTPase activity at concentrations higher than 0.5 M.

Creating new restriction sites by silent changes in coding sequences

We present methods for identifying a useful type of DNA site--one that can be mutated to create a new restriction site within a coding region without changing the amino acid sequence. These "latent sites" are abundant--silent mutations creating one of 44 different 6-bp or 8-bp recognition sites were found at relatively high density, roughly one latent site per 9 bp, in the eleven genes tested. Our analysis suggests that site-directed mutagenesis can be used to refashion coding sequences at will for flexible analysis.

Biological properties of human c-Ha-ras1 genes mutated at codon 12

Vertebrate genomes contain proto-oncogenes whose enhanced expression or alteration by mutation seems to be involved in the development of naturally occurring tumours. These activated genes, usually assayed by their ability to induce the malignant transformation of NIH 3T3 cells, are frequently related to the ras oncogene of Harvey (Ha-ras) or Kirsten (Ki-ras) murine sarcoma viruses, or a third member of this family (N-ras). Activation involves point mutation which often affect codon 12 (refs 16-26) of the encoded 21,000-molecular weight polypeptide (p21). To provide insight into structural requirements involved in p21 activation, we have now constructed 20 mutant c-Ha-ras1 genes by in vitro mutagenesis, each encoding a different amino acid at codon 12. Analysis of rat fibroblasts transfected with these altered genes demonstrates that all amino acids except glycine (which is encoded by normal cellular ras genes) and proline at position 12 activate p21, suggesting a requirement for an alpha-helical structure in this region of the polypeptide. The morphological phenotype of cells transformed by the activated genes can, however, depend on the particular amino acid at this position.

Harvey murine sarcoma virus p21 ras protein: biological and biochemical significance of the cysteine nearest the carboxy terminus

Previous studies of premature chain termination mutants and in frame deletion mutants of the p21 ras transforming protein encoded by the transforming gene of Harvey murine sarcoma virus (Ha-MuSV) have suggested that the C terminus is required for cellular transformation, lipid binding, and membrane localization. We have now further characterized the post-translational processing of these mutants and have also studied two C-terminal v-rasH point mutants: one encodes serine in place of cysteine-186, the other threonine for valine-187. The Thr-187 mutant was transformation-competent, and its p21 protein was processed normally, as was the p21 encoded by a transformation-competent deletion mutant from which amino acids 166-175 had been deleted. The Ser-186 mutant was defective for transformation. The p21s encoded by the Ser-186 mutant and by the previously described transformation-defective mutants did not undergo the posttranslational processing common to biologically active ras proteins: their electrophoretic migration rate did not change, they remained in the cytosol, and they failed to bind lipid. Since the cell-encoded ras proteins also contain this cysteine, we conclude that this amino acid residue is required for all ras proteins.

Further characterization of the P85gag-mos -associated protein kinase activity

The gag-mos hybrid protein encoded by ts110 MoMuSV was shown to have an associated protein kinase activity which phosphorylated both P85gag-mos and P58gag when [gamma-32P]ATP and a manganese cofactor were added to an immune complex containing P85gag-mos. Immunoprecipitation and removal of P85gag-mos from the reaction mixture by either an anti-mos or anti-gag serum resulted in a subsequent elimination of in vitro P85gag-mos and P58gag phosphorylation. This kinase activity was shown to be either an intrinsic property of P85gag-mos or else a tightly bound cellular enzyme activity resistant to elution with 2.0 M NaCl, 0.5% deoxycholate, and 0.1% SDS. A correlation was made between the amount of kinase activity and the concentration of P85gag-mos. Viral gag antisera were also used to show immune complex phosphorylation of another gag-mos hybrid protein termed P100gag-mos, derived from a revertant of ts110. In vitro phosphorylation experiments derived from v-mos transformed MuSV 124 cells using viral gag antisera were completely negative which shows that the gag-mos kinase in 6m2 cells is not merely a gag-associated kinase that phosphorylates MuSV coded gag gene products. When shifting 6m2 cells from a permissive temperature to the nonpermissive temperature of 39 degrees for 2-4 hr, a noticeable change toward a more normal morphology occurs. NRK 54-5A4 cells infected with a revertant of ts110 with wild-type phenotype, showed little change in morphology between permissive and nonpermissive temperatures. In addition to the ts defect affecting P85gag-mos production previously reported, a second ts defect in ts110 is reported here which is functional in nature; it can be detected within 5 min after shift to 39 degrees by the heat lability of the P85-associated kinase activity. The P100gag-mos protein kinase from the wild-type revertant cells did not exhibit this heat sensitivity under similar conditions. The thermal inactivation of the P85 kinase was shown to precede events that occur as cells are shifted to the restricted temperature including morphological reversion to the normal phenotype, and the decrease in P85gag-mos concentration. Based on all of these observations, it is suggested that the P85-associated kinase activity is not merely an adherent cellular kinase, but actually a function of the gag-mos gene product.

Transcription of two classes of rat growth hormone gene-associated repetitive DNA: differences in activity and effects of tandem repeat structure

The rat growth hormone (rGH) gene contains two classes of repetitive DNA arranged as clusters within intron B and the 3' flanking region. The major family is equivalent to the CHO type 2 DNA. The second ("truncated repeat", TR) is a truncated version of the first and occurs in certain neural-specific transcripts and genes ("identifier" elements, ID). Here we report, using the HeLa cell-free transcription assay, that RNA polymerase III (Pol III) efficiently initiates at internal promoters within a tandem array of rGH gene repetitive DNA monomers and results in a novel organization of overlapping Class III transcription units. Transcription competition studies revealed that the rat type 2 structures share Pol III transcription factors with a tRNA gene, a human Alu repeat, and a mutant VA1 gene. Also, the rGH type 2 but not the TR DNA efficiently promotes Pol III initiation, yet other TR members, which differ only in flanking DNA, are transcribed. Thus, the rGH gene is strikingly enriched with 10 repetitive DNA monomers; multimeric type 2 elements are actively transcribed; rGH-TR sequences are expressed only as part of larger transcripts promoted by type 2 DNA; and, type 2 DNA uses tRNA gene transcription factors. These studies show that flanking sequences, promoter organization and factor competition may all affect rat repetitive DNA expression.

Homologies between a brain-specific identifier (ID) sequence and regions of Harvey murine sarcoma virus and Rous sarcoma virus genomes. Putative role of identifier sequences in the tissue specificity of malignant transformation by RNA tumor viruses

As a step toward understanding of the tissue specificity of cellular transformation by RNA tumor viruses were looked for the presence of a putative brain specific regulatory (identifier) sequence (C82B) in the genome of various oncornaviruses. The genomes of Harvey murine sarcoma virus and Rous sarcoma virus contain sequences flanking the viral oncogenes with greater than 80% and greater than 60% homology to C82B, respectively. We suggest that identifier sequences acquired by oncoviruses may determine the potential target cells of malignant transformation after virus penetration.

Expression of normal and transforming H-ras genes in Escherichia coli and purification of their encoded p21 proteins

The H-ras gene of the BALB murine sarcoma virus (BALB-MSV) was placed under the transcriptional control of the tightly regulated PL promoter of bacteriophage lambda in the expression vectors pEV-vrf-1 and pRC23. Upon derepression of the PL promoter, large amounts (10-20% of total cellular protein) of the H-ras gene product p21 are synthesized in Escherichia coli. We constructed three H-ras gene expression vectors, designated pJCL-H5, pJCL-E30, and pJCL-33. pJCL-H5 directs the synthesis of p21, a fusion protein whose four amino-terminal residues are replaced by eight amino acids coded for by plasmid sequences. The 13 5' coding nucleotides of the BALB-MSV H-ras gene missing in pJCL-H5 were regenerated in pJCL-E30 by inserting a pair of complementary synthetic oligodeoxynucleotides. As a result, pJCL-E30 encodes a p21 protein, p21T, of sequence identical to that of the transforming p21 protein of BALB-MSV. pJCL-33 is a derivative of pJCL-E30 in which the 12th codon, AAA, a lysine codon, was replaced by GGA, a glycine codon. Thus, pJCL-33 directs the synthesis of a p21 protein, p21N, whose sequence corresponds to that of a normal cellular p21 protein. We report the purification of H-ras p21 proteins to apparent homogeneity by a method involving solubilization with chaotropic agents followed by reverse-phase high-performance liquid chromatography.

The p21 ras C-terminus is required for transformation and membrane association

The Harvey murine sarcoma virus (Ha-MuSV) transforming gene, v-rasH, encodes a 21,000 molecular weight protein (p21) that is closely related to the p21 proteins encoded by the cellular transforming genes of the ras gene family. The primary translation product (prop21), which is found in the cytosol, undergoes posttranslational modification and the mature protein subsequently becomes associated with the inner surface of the plasma membrane and binds lipid tightly. The p21 proteins have the capacity to bind guanine nucleotides non-covalently in vitro. To assess the biological relevance of these biochemical features of the protein, we have now studied a series of deletion mutants located at or near the C-terminus of the viral p21 protein. Our tissue culture studies indicate that amino acids located at or near the C-terminus are required for cellular transformation, membrane association and lipid binding.

An activated rasN gene: detected in late but not early passage human PA1 teratocarcinoma cells

Early passages of the human teratocarcinoma cell line PA1 are not tumorigenic in nude mice, while late passages are. A transforming gene present in late passages of PA1 cells was isolated as a biologically active molecular clone and is a new isolate of the human rasN locus. Its transforming activity is due to a single G---A (G, guanine; A, adenine) point mutation at the codon for amino acid 12 which changes the codon for glycine so that an aspartic acid residue is expressed. In contrast to late passage PA1 cells (passages 106, 330, and 338), DNA from the PA1 cell line at early passages (passage 36) does not yield rasN foci in DNA transfection assays. Thus, the presence of an activated rasN in PA1 cells correlates with enhanced tumorigenicity of the cell line and, more importantly, may have arisen during cell culture in vitro.

Transformation of NIH 3T3 cells by microinjection of Ha-ras p21 protein

Alteration in gene structure has been shown to occur in some human tumours. These altered genes, termed oncogenes, were originally identified by their ability to induce foci of transformed cells on transfected mouse 3T3 cultures. The oncogene identified in the EJ/T24 human bladder carcinoma is similar to the transforming gene of BALB and Harvey murine sarcoma virus (MSV) and differs from its counterpart in normal cells by a single amino acid. All three of these Ha-ras genes direct the production of similar proteins (p21). While the ras gene appears to be involved in tumour formation in some situations, its role is unclear. The ras protein product (p21) binds guanine nucleotides and has a unique autophosphorylating activity, but no other enzymatic activity has been found. We report here the injection of purified Ha-ras p21 protein, made in Escherichia coli from the gene of BALB-MSV, into NIH 3T3 cells and show that the purified protein itself is sufficient to induce a transformed morphology. In addition, the injected protein stimulates quiescent cells to enter the S-phase of the cell cycle. This result clearly demonstrates that the ras gene functions directly through the protein product. It also establishes an assay for the protein which depends on its activity within a living cell. The transforming activity of a p21 ras protein equivalent to the product of the normal cellular ras gene, is also demonstrated.

Three steps mutation model of carcinogenesis

Based on recent data, this model supposes that benign and malignant tumors arise when a specific mutation takes place in a specific protein-kinase encoded by a proto-oncogene in a pluripotent stem cell or a committed stem cell. Protein-kinases which are regulated by tissue growth stimulating factors, tissue growth inhibiting factors and differentiating factors phosphorylate specific proteins that can derepress specific genes leading to cell division and cell differentiation. Malignant tumors arise when three mutations happen in a same pluripotent stem cell or committed stem cell: positive mutation at the level of tissue growth stimulating factor; negative mutation at the level of tissue growth inhibiting factor; negative mutation at the level of tissue differentiating factor. Higher expression of oncogenes and amplification reflect the relationship between tumor and host. Chromosomal rearrangements are secondary events that can be important because they may involve genes which are normally not involved in cell division and cell differentiation.

An altered DNA sequence encompassing the ras gene of Harvey murine sarcoma virus

The DNA fragment encompassing the ras gene of Harvey murine sarcoma virus was sequenced and assigned the coding region of a transforming protein, p21, to the sequence. Examination of nucleotide sequence, taken together with the result of analysis of the ras mRNAs (1), has revealed that p21 is encoded from a continuous coding region starting with the 5' proximal initiation codon but not a processed protein. However, there were found several differences between the sequence published by Dhar et. al. (2) and ours, including 9 deletions, 7 substitutions and 2 insertions of nucleotides in the published sequence of 997 nucleotides in length. Among these, one of the substitutions occurring in the coding region resulted in amino acid replacement of glycine by alanine at position 122 of p21. The evidences are presented with some of actual gel autoradiographs.

Analysis of the transforming potential of the human H-ras gene by random mutagenesis

Some tumor cells contain mutant ras genes that are capable of transforming NIH 3T3 cells. Those genes that have been analyzed arise from the wild-type, non-transforming ras genes by mutations producing single amino acid substitutions at position 12 or 61 of the encoded protein. We have performed random bisulfite-induced mutagenesis on the cloned wild-type human H-ras gene to find if mutations at other positions can activate the transforming potential of that gene. Most mutations are not activating, but mutations that specify single amino acid substitutions at position 12, 13, 59, or 63 of the encoded protein do activate the transforming potential of the H-ras gene. Some, but not all, mutant ras proteins show an altered electrophoretic mobility in NaDodSO4/polyacrylamide gels.

The Drosophila ras oncogenes: structure and nucleotide sequence

Three Drosophila genes homologous to the Ha-ras probe were isolated and mapped to positions 85D, 64B, and 62B on chromosome 3. Two of these genes (termed Dras 1 and Dras 2) were sequenced. In the case of Dras 1, which contains multiple introns, a cDNA clone was isolated and sequenced. In the case of Dras2, the nucleotide sequence fo the genomic clone was determined. Each gene codes for a protein with a predicted molecular weight of 21.6 kd. Alignment of the amino acid sequence of Dras 1 with the vertebrate Ha-ras protein shows that at the amino terminus and central portion (residues 1-121 and 137-164) the two proteins are remarkably similar, and have an overall homology of 75%. The Dras 2 gene lacks significant homology to the vertebrate counterpart at the extreme amino terminus and is homologous only between positions 28-120 and 139-161 (overall homology of 50%). This result suggests that the N terminus of p21 forms a distinct regulatory or functional domain. At the carboxy terminus, the major region of variability among the vertebrate ras proteins, the two Drosophila sequences also display considerable variability. However, both appear to be more similar to exon 4B of the Ki-ras gene.

RNA polymerase III control regions in retrovirus LTR, Alu-type repetitive DNA, and papovavirus

Sequences analogous to the intragenic bipartite RNA polymerase III promoter regions in tRNA genes, are described in mammalian Alu-type repetitive DNA, LTR of retroviruses and control regions of papovaviruses. The RNA polymerase III control regions in some of these DNA elements are present in enhancer sequences which are known to increase the transcription of RNA polymerase II transcribed genes. It is suggested that the host and tissue specificity of the enhancer elements may be explained by differences in the RNA polymerase III control sequences. The RNA polymerase III promoters may thus participate in regulation of cell differentiation and transcription of tissue specific genes.

Photoaffinity labeling with GTP of viral p21 ras protein expressed in Escherichia coli

The v-ras oncogene of Harvey murine sarcoma virus encodes a 21,000-dalton protein, p21, which mediates transformation produced by that virus. Previous work has shown that both p21v-rasH and the cellular homolog p21c-rasH appear to bind guanine nucleotides. We report here the expression in Escherichia coli of v-rasH to produce a biochemically active p21 fusion protein which retains both guanine nucleotide binding and autophosphorylating activity. Furthermore, direct interaction of this protein with GTP is unequivocally demonstrated by photoaffinity labeling it with [alpha-32P]GTP.

Nucleotide sequence of v-fps in the PRCII strain of avian sarcoma virus

PRCII is an avian retrovirus whose oncogene (v-fps) induces fibrosarcomas in birds. The viral gene v-fps arose by transduction of an undetermined portion of a cellular gene known as c-fps. PRCII is weakly oncogenic when compared with Fujinami sarcoma virus, another transforming virus containing v-fps. As a first step in the elucidation of the molecular basis for the decreased virulence of PRCII, we have determined the entire nucleotide sequence of v-fps in the PRCII genome. The v-fps domain in PRCII encodes a polypeptide with a molecular weight of ca. 60,500 fused to a portion of the polyprotein encoded by the viral structural gene gag. The hybrid gag-fps polyprotein of PRCII would have a molecular weight of ca. 98,100, in accord with results of previous studies of the protein encoded by the PRCII genome. The leftward junctions between fps and gag in Fujinami sarcoma virus and PRCII are located at the same position in fps, but at different positions in gag. A sequence of 1,020 nucleotides, bounded by direct repeats of 6 nucleotides, is present in v-fps of Fujinami sarcoma virus but absent from PRCII. Our data should permit further explorations of the relationship between structure and function in the transforming protein encoded by v-fps.

Myristylation of gag-onc fusion proteins in mammalian transforming retroviruses

Four cell lines producing transforming proteins encoded by three mammalian oncogenes (fes, abl, and ras) were investigated for incorporation of [3H]myristate into gag-onc fusion proteins. Using 5-min pulse-labelings, fusion proteins of Abelson murine leukemia virus, Gardner-Arnstein strain of feline sarcoma virus (FeSV), and Snyder-Theilen strain of FeSV were shown to be myristylated. In a 4-hr pulse, p29gag-ras of rat sarcoma virus (RaSV) was also shown to incorporate radiolabel. The fatty acid was recovered from this labeled protein by acid hydrolysis, and identified by reverse-phase thin-layer chromatography to be [3H]myristic acid. The results indicate that substitution of viral gag sequences by cellular oncogene sequences does not abolish their ability to become post-translationally modified by this long chain fatty acid (A. Schultz and S. Oroszlan, J. Virol. 46, 355-361). It is assumed that in the fusion proteins the myristyl moiety is linked through an amide linkage to the amino-terminal glycine as previously found for several retroviral gag precursor polyproteins (L. E. Henderson, H. C. Krutzsch, and S. Oroszlan, Proc. Natl. Acad. Sci. USA 80, 339-343). The possible role of myristylation of transforming proteins is discussed.

The human c-Ha-ras2 is a processed pseudogene inactivated by numerous base substitutions

The human c-Ha-ras2 gene, one of two known members of the Harvey ras family, is reportedly located on the X-chromosome and has lost introns (1, 2). There has heretofore been no information on its precise gene structure and oncogenic potential. We have determined the nucleotide sequence of the c-Ha-ras2 and demonstrate that it is a processed pseudogene surrounded by several direct repeats and contains numerous base substitutions as well as a notable mutation (AGT at codon 12 of the p21 protein) responsible for oncogenic conversion of the known ras genes (3-8).

Glucocorticoid regulation of transcription at an amplified, episomal promoter

The mouse mammary tumor virus long terminal repeat (MMTV LTR) has been introduced into cultured murine cells, using the 69% transforming fragment of bovine papilloma virus type 1 (BPV). Transformed cells contain up to 200 copies of the chimeric molecules per diploid genome. The restriction endonuclease map of the acquired recombinants, as well as the physical structure of the DNA, indicates that the LTR-BPV molecules present in these cells occur exclusively as unintegrated, extrachromosomal episome. When a 72-base pair direct repeat "enhancer" element (derived from the Harvey sarcoma retrovirus) was included in the MMTV LTR-BPV chimeric plasmids, DNA acquired through transfection, with a single exception, was integrated or rearranged or both. The transcriptional potential of the episomal MMTV promoter present in these cells was tested in two ways. First, steady-state levels of MMTV-initiated RNA were measured by quantitative S1 mapping. Second, the relative number of transcription complexes initiated in vivo was determined by using a subnuclear fraction highly enriched for MMTV-BPV minichromosomes in an in vitro transcription extension assay. Both approaches showed that the MMTV LTR present in the episomal state was capable of supporting glucocorticoid hormone-regulated transcription. We have therefore demonstrated the hormone response for the first time in a totally defined primary sequence environment. Significant differences both in the basal level of MMTV-initiated transcription and in the extent of glucocorticoid induction were observed in individual cell lines with similar episomal copy numbers. These phenotypic variations suggest that epigenetic structure is an important component of the mechanism of regulation.

Further genetic localization of the transforming sequences of the p21 v-ras gene of Harvey murine sarcoma virus

The sequences encoding the 21-kilodalton transforming protein (p21 ras) of Harvey murine sarcoma virus have previously been localized genetically to a 1.3-kilobase segment of the viral DNA (E. H. Chang, R. W. Ellis, E. M. Scolnick, and D. R. Lowy, Science 210:1249-1251, 1980). Within this segment, DNA sequence analysis has found a single open reading frame large enough to encode the viral p21 (R. Dhar, R. W. Ellis, T. Y. Shih, S. Oroszlan, B. Shapiro, J. Maizel, D. Lowy, and E. M. Scolnick, Science 217:934-937, 1982). There are three potential in-frame ATG initiation codons at the 5' end of this open reading frame. By constructing a mutant of Harvey murine sarcoma virus DNA from which the first two ATG codons of this open reading frame have been deleted, we now show by transfection of the mutant viral DNA into NIH 3T3 cells that only the third ATG codon is necessary and sufficient for synthesis of the viral p21 and for cellular transformation.

Brain-specific genes have identifier sequences in their introns

The 82-nucleotide identifier (ID) sequence is present in the rat genome in 1-1.5 X 10(5) copies and in cDNA clones of precursors of brain-specific mRNAs. One brain-specific gene contains more than one ID sequence in its introns. There is an excess of ID sequences to brain genes, and some ID sequences appear to have been inserted as mobile elements into other genetic locations. Therefore, brain genes contain ID sequences in their introns, but not all ID sequences are located in brain gene introns. A brain ID consensus sequence has been obtained by comparing 8 ID nucleotide sequences.

Homologies in the primary structure of GTP-binding proteins: the nucleotide-binding site of EF-Tu and p21

An examination of the available amino acid sequences of GTP-binding proteins has revealed that each contains a polypeptide essentially homologous for all of them. These sequences for elongation factor-Tu (EF-Tu) and the human bladder protein p21 exhibit a singular degree of homology (50%). Chemical and structural evidence indicates that this sequence in EF-Tu constitutes part of the nucleotide-binding site. The homologous sequences may therefore contribute to the GTP-binding sites of the other proteins.

RNA-tumorviruses, oncogenes, and their possible role in human carcinogenesis

The detection and characterization of oncogenes via RNA tumor viruses (or retroviruses) and the recognition of their location at breakpoints of chromosomal translocations which are frequently found in certain human neoplasms has promoted present understanding of molecular mechanisms underlying carcinogenesis. Oncogenes are cellular genes which can be transduced by RNA tumorviruses and induce malignant transformation under experimental conditions in vivo and in vitro. A role of retroviruses in human leukemogenesis is suggested by epidemiological observations and by the isolation of such viruses from several human T-cell leukemias and lymphomas (human T-cell leukemia/lymphoma virus or HTLV) as well as by biochemical association of retroviral markers with human leukemias. A role of HTLV has been suggested also in a human immune deficiency syndrome (AIDS). In view of the well known role of many factors in carcinogenesis the concept of carcinogenesis as a multistep process as well as the concept of cocarcinogenesis and the role of cofactors other than viruses, such as radiation and chemicals, aging, hormones, graft vs host reaction, environmental factors etc., will have to be carefully considered.

ras-Related gene sequences identified and isolated from Saccharomyces cerevisiae

The oncogenes of Harvey and Kirsten murine sarcoma viruses (v-rasH and v-rasK) and their cellular homologues (c-rasH and c-rasK) constitute two members of the ras gene family. Each functional member of the ras gene family encodes a 21,000 molecular weight protein (p21ras). ras genes have been detected in a wide variety of vertebrate species, including Xenopus laevis (R. E. Steele, personal communication), and in Drosophila melanogaster. We report here the detection of ras-related genes in the yeast Saccharomyces cerevisiae, and the isolation of two ras-related molecular clones, c-rassc-1 and c-rassc-2, from the DNA of Saccharomyces. Both c-rassc-1 and c-rassc-2 hybridize specifically to probes prepared from mammalian ras DNA. Sequencing of c-rassc-1 reveals extensive amino acid homology between the protein encoded by c-rassc-1 and the p21 encoded by c-rasH. Our studies suggest that these clones can be used to elucidate the normal cellular functions of ras-related genes in this relatively simple eukaryotic organism.

A yeast gene encoding a protein homologous to the human c-has/bas proto-oncogene product

Organisms amenable to easy genetic analysis should prove helpful in assessing the function of at least those proto-oncogene products which are highly conserved in different eukaryotic cells. One obvious possibility is to pursue the matter in Drosophila melanogaster DNA, which has sequences homologous to several vertebrate oncogenes. Another is to turn to the yeast Saccharomyces cerevisiae, if it contains proto-oncogene sequences. Here we report the identification of a gene in S. cerevisiae which codes for a 206 amino acid protein (YP2) that exhibits striking homology to the p21 products of the human c-has/bas proto-oncogenes and the transforming p21 proteins of the Harvey (v-rasH) and Kirsten (v-rasK) murine sarcoma viral oncogenes. The YP2 gene is located between the actin and the tubulin gene on chromosome VI and is expressed in growing cells. The protein it encodes might share the nucleotide-binding capacity of p21 proteins.

Regional chromosomal localization of N-ras, K-ras-1, K-ras-2 and myb oncogenes in human cells

The identification of transforming genes in human tumor cells has been made possible by DNA mediated gene transfer techniques. To date, it has been possible to show that most of these transforming genes are activated cellular analogues of the ras oncogene family. To better understand the relationship between these oncogenes and other human genes, we have determined their chromosomal localization by analyzing human rodent somatic cell hybrids with molecularly cloned human proto-oncogene probes. It was possible to assign N-ras to chromosome 1 and regionally localize c-K-ras-1 and c-K-ras-2 to human chromosomes 6pter-q13 and 12q, respectively. These results along with previous studies demonstrate the highly dispersed nature of ras genes in the human genome. Previous reports indicated that the c-myb gene also resides on chromosome 6. It has been possible to sublocalize c-myb to the long arm of chromosome 6 (q15-q21). The non-random aberrations in chromosomes 1, 6 and 12 that occur in certain human tumors suggest possible etiologic involvement of ras and/or myb oncogenes in such tumors.

Cellular oncogenes and multistep carcinogenesis

Two dozen cellular proto-oncogenes have been discovered to date through the study of retroviruses and the use of gene transfer. They form a structurally and functionally heterogeneous group. At least five distinct mechanisms are responsible for their conversion to active oncogenes. Recent work provides experimental strategies by which many of these oncogenes, as well as oncogenes of DNA tumor viruses, may be placed into functional categories. These procedures may lead to definition of a small number of common pathways through which the various oncogenes act to transform cells.

Glucocorticoid regulation of transcription at an amplified, episomal promoter

The mouse mammary tumor virus long terminal repeat (MMTV LTR) has been introduced into cultured murine cells, using the 69% transforming fragment of bovine papilloma virus type 1 (BPV). Transformed cells contain up to 200 copies of the chimeric molecules per diploid genome. The restriction endonuclease map of the acquired recombinants, as well as the physical structure of the DNA, indicates that the LTR-BPV molecules present in these cells occur exclusively as unintegrated, extrachromosomal episome. When a 72-base pair direct repeat "enhancer" element (derived from the Harvey sarcoma retrovirus) was included in the MMTV LTR-BPV chimeric plasmids, DNA acquired through transfection, with a single exception, was integrated or rearranged or both. The transcriptional potential of the episomal MMTV promoter present in these cells was tested in two ways. First, steady-state levels of MMTV-initiated RNA were measured by quantitative S1 mapping. Second, the relative number of transcription complexes initiated in vivo was determined by using a subnuclear fraction highly enriched for MMTV-BPV minichromosomes in an in vitro transcription extension assay. Both approaches showed that the MMTV LTR present in the episomal state was capable of supporting glucocorticoid hormone-regulated transcription. We have therefore demonstrated the hormone response for the first time in a totally defined primary sequence environment. Significant differences both in the basal level of MMTV-initiated transcription and in the extent of glucocorticoid induction were observed in individual cell lines with similar episomal copy numbers. These phenotypic variations suggest that epigenetic structure is an important component of the mechanism of regulation.

The erbB gene of avian erythroblastosis virus is a member of the src gene family

The erbB gene of an avian erythroblastosis virus, AEV-H, was determined to be 1812 nucleotides long and was predicted to code for a protein of 67,638 daltons. Unexpectedly, a sequence of 285 amino acids in the middle of the protein showed a significant homology (38%) with the sequence in the carboxy terminus of p60src. The nucleotide sequence of a mutant of AEV-H, td-130, which induces sarcomas but not erythroblastosis in chicken, was also analyzed. A deletion of 169 nucleotides was identified in the 3' half of the erbB gene, indicating that the gene codes for a truncated protein with the predicted molecular weight of 46,667. These findings suggest that the homologous domain of erbB protein with its N-terminal portion is sufficient for the transformation of fibroblasts and that one-third of the carboxy-terminal domain has a key role for the transformation of erythroid cells.

Structure and activation of the human N-ras gene

The normal human N-ras gene has been cloned. In structure and sequence it closely resembles the human H-ras and K-ras genes. The three genes share regions of nucleotide homology and nucleotide divergence within coding sequences and have a common intron/exon structure, indicating that they have evolved from a similarly spliced ancestral gene. The N-ras gene of SK-N-SH neuroblastoma cells has transforming activity, while the normal N-ras gene does not, the result of a single nucleotide change substituting lysine for glutamine in position 61 of the N-ras gene product. From previous studies we conclude that amino acid substitutions in two distinct regions can activate the transforming potential of ras gene products.

Prediction of the three-dimensional structure of the transforming region of the EJ/T24 human bladder oncogene product and its normal cellular homologue

The three-dimensional structures of the transforming region of the product of the EJ/T24 human bladder oncogene and of the c-Ha ras-1 gene product have been calculated by using conformational energy calculations. These two genes, representing a transforming oncogene and its normal cellular homologue, encode 21,000-dalton peptides that differ by one amino acid at position 12. We therefore examined the energetically allowed conformations of the hydrophobic decapeptide surrounding this substitution site. The calculations show that the most favorable form of the c-Ha ras-1 gene product exists when glycine-12 is in a left-handed bend conformation. No other amino acid can adopt this conformation and thus the bladder oncogene peptide containing valine at position 12 has a markedly different three-dimensional structure. A simple model is proposed to account for the consequences of a position 12 mutation.

Flat revertants isolated from Kirsten sarcoma virus-transformed cells are resistant to the action of specific oncogenes

Two flat revertants have been isolated from mutagen-treated populations of Kirsten murine sarcoma virus (Ki-MuSV)-transformed NIH/3T3 cells. These revertants, which appear to be cellular variants resistant to transformation by the Ki-MuSV oncogene v-Ki-ras, contain Ki-MuSV-specific DNA, elevated levels of the v-Ki-ras gene product p21, and rescuable transforming virus. Cell hybridization studies indicated that the revertant phenotype is dominant in hybrids between revertant cells and cells transformed by Ki-MuSV or the closely related Harvey MuSV and BALB MuSV. Analysis of hybrid cells resulting from the fusion of these revertants to cell lines transformed by other retroviruses showed that the action of certain oncogenes structurally unrelated to v-Ki-ras also could be suppressed. Thus, there appear to be functional relationships and diversities among transforming genes (oncogenes) not readily apparent from their structural characteristics.

High-level expression in Escherichia coli of enzymatically active Harvey murine sarcoma virus p21ras protein

The gene for the Harvey murine sarcoma virus (Ha-MuSV) p21ras protein was fused to the amino-terminal portion of the bacteriophage lambda cII gene on the expression vector pJL6. The fusion was such that transcription was controlled by the well-regulated phage lambda pL promoter, and translation initiated in the cII gene continued in frame into the ras gene sequences that code for p21. When the pL promoter was derepressed, the Escherichia coli cells harboring the fusion plasmid synthesized 23,000-dalton protein, which represented more than 10 percent of the total cellular protein. This protein was chimeric and contained 14 residues, which were specified by the vector; these residues were followed by all of the amino acids that make up Ha-MuSV p21ras except for four residues at the amino-terminal end. The protein appears similar to Ha-MuSV p21ras in that it undergoes immunoprecipitation by monoclonal antibodies directed toward that protein, binds guanosine diphosphate, and is capable of autophosphorylation.