Molecular organization of the chicken ets locus

ETS family of genes in leukemia and Down syndrome

The human ETS2 and ERG genes are members of the ETS gene family, with sequence homology to the viral ets gene of the avian erythroblastosis retrovirus, E26. These genes are located on chromosome 21 and molecular genetic analysis of Down syndrome (DS) patients with partial trisomy 21 suggested that ETS2 may be a gene within the minimal DS genetic region. We have, in fact, been able to confirm the presence of the ETS2 gene dosage in triplicate occurring in occult human 21 chromosome abnormalities. It is known that ERG and ETS2 gene translocations occur in certain specific leukemias associated with defined chromosome rearrangements [e.g., t(8;21)]. Moreover, it is known that DS individuals are at greater risk for leukemic disease than their normal familial cohorts, implying that trisomy of that region of human chromosome 21 may play a role in the development of this type of neoplasia. The human ETS genes, first identified in our laboratory, are highly conserved, being found from lower organisms, like Drosophila and sea urchin, to humans. In mammals, the ETS genes are structurally distinct, located on separate chromosomes; they are transcriptionally active and differentially regulated. The ETS2 protein is phosphorylated and turns over with a half-life of approximately 20 min. After activation with the tumor promoter, TPA, the level of ETS2 elevates 5- to 20-fold. The properties of the ETS2 protein, such as nuclear localization, phosphorylation, rapid turnover, and response to protein kinase C, indicate that this protein belongs to a group of oncogene proteins thought to have regulatory functions in the nucleus. In the mouse thymus ets-1 and ets-2 are 8-10-fold higher, respectively, in the CD4+ subset than in other subsets examined, suggesting a role in T-cell development for these genes. Cells transfected with the cellular ets-2 gene, expressing higher levels of ets-2 products, showed a stimulated proliferation response, abolished their serum requirement and formed colonies in soft agar that could induce tumors in nude mice. Collectively, these data suggest that this family of genes might play a role in controlling specific steps of the signaling transduction pathway. Thus, the ETS genes, as other genes with homology to viral oncogenes, might be instrumental in regulating cellular growth and differentiation, as well as organismal development.

Exon 4-encoded acidic domain in the epithelium-restricted Ets factor, ESX, confers potent transactivating capacity and binds to TATA-binding protein (TBP)

The Ets gene family has a complex evolutionary history with many family members known to regulate genetic programs essential for differentiation and development, and some known for their involvement in human tumorigenesis. To understand the biological properties associated with a recently described epithelium-restricted Ets factor ESX, an 11 kb fragment from the 1q32.2 genomically localized human gene was cloned and analysed. Upstream of the ESX promoter region in this genomic fragment lies the terminal exon of a newly identified gene that encodes a ubiquitin-conjugating enzyme variant, UEV-1. Tissues expressing ESX produce a primary 2.2 kb transcript along with a 4.1 kb secondary transcript arising by alternate poly(A) site selection and uniquely recognized by a genomic probe from the 3' terminal region of the 11 kb clone. Endogenous expression of ESX results in a 42 kDa nuclear protein having fivefold greater affinity for the chromatin-nuclear matrix compartment as compared to other endogenous transcription factors like AP-2 and the homologous Ets factor, ELF-1. Exon mapping of the modular structure inferred from ESX cDNA and construction of GAL4(DBD)-ESX expression constructs were used to identify a transactivating domain encoded by exon 4 having comparable potency to the acidic transactivation domain of the viral transcription factor, VP16. This exon 4-encoded 31 amino acid domain in ESX was shown by mutation and deletion analysis to possess a 13 residue acidic transactivation core which, based on modeling and circular dichroism analysis, is predicted to form an amphipathic alpha-helical secondary structure. Using recombinant GST-ESX (exon 4) fusion proteins in an in vitro pull-down assay, this ESX transactivation domain was shown to bind specifically to one component of the general transcription machinery, TATA-binding protein (TBP). Transient transfection experiments confirmed the ability of this TBP-binding transactivation domain in ESX to squelch heterologous promoters independent of any promoter binding as efficiently as the transactivation domain from VP16.

Myb-Ets fusion oncoprotein inhibits thyroid hormone receptor/c-ErbA and retinoic acid receptor functions: a novel mechanism of action for leukemogenic transformation by E26 avian retrovirus

The E26 and avian erythroblastosis virus (AEV) avian retroviruses induce acute leukemia in chickens. E26 can block both erythroid and myeloid differentiation at an early multipotent stage. Moreover, E26 can block erythroid differentiation at the erythroid burst-forming unit/erythroid CFU (BFU-E/CFU-E) stage, which also corresponds to the differentiation stage blocked by AEV. AEV carries two oncogenes, v-erbA and v-erbB, whereas E26 encodes a single 135-kDa Gag-Myb-Ets fusion oncoprotein. v-ErbA is responsible for the erythroid differentiation arrest through negative interferences with both the retinoic acid receptor (RAR) and the thyroid hormone receptor (T3R/c-ErbA). We investigated whether Myb-Ets could block erythroid differentiation in a manner similar to v-ErbA. We show here that Myb-Ets inhibits both RAR and c-ErbA activities on specific hormone response elements in transient-expression assays. Moreover, Myb-Ets abrogates the inactivation of transcription factor AP-1 by RAR and T3R, another feature shared with v-ErbA. Myb-Ets also antagonizes the biological response of erythrocytic progenitor cells to retinoic acid and T3. Analysis of a series of mutants of Myb-Ets reveals that the domains of the oncoprotein involved in these inhibitory activities are the same as those involved in oncogenic transformation of hematopoietic cells. These data demonstrate that the Myb-Ets oncoprotein shares properties with the v-ErbA oncoprotein and that inhibition of ligand-dependent RAR and c-ErbA functions by Myb-Ets is responsible for blocking the differentiation of hematopoietic progenitors.

Effects of provirus integration in the Tpl-1/Ets-1 locus in Moloney murine leukemia virus-induced rat T-cell lymphomas: levels of expression, polyadenylation, transcriptional initiation, and differential splicing of the Ets-1 mRNA

The Tpl-1 locus was defined as a genomic DNA region which is targeted by provirus insertion during progression of Moloney murine leukemia virus-induced rat T-cell lymphomas. Using a panel of 156 (Mus musculus x Mus spretus) x Mus musculus interspecific backcross mice, we mapped Tpl-1 to mouse chromosome 9 at a distance of 1.2 +/- 0.9 centimorgans from the Ets-1 proto-oncogene (S.E. Bear, A. Bellacosa, P.A. Lazo, N.A. Jenkins, N.G. Copeland, C. Hanson, G. Levan, and P.N. Tsichlis, Proc. Natl. Acad. Sci. USA 86:7495-7499, 1989). In this report, we present evidence that all the known Tpl-1 provirus insertions occurred immediately 5' of the first exon of Ets-1 (exon A) and that the earlier detected distance between Tpl-1 and Ets-1 was due to the high frequency of meiotic recombination in the region between the site of provirus integration and exon III. Northern (RNA) blot analysis of polyadenylated RNA from normal adult rat tissues and Moloney murine leukemia virus-induced T-cell lymphomas and hybridization to a Tpl-1/Ets-1 probe derived from the 5' end of the gene revealed two lymphoid cell-specific RNA transcripts, of 5.5 and 2.2 kb. Sequence analysis of a near-full-length (4,991-bp) cDNA clone of the 5.5-kb RNA revealed a 441-amino-acid open reading frame encoding a protein identical to the human and mouse Ets-1 proteins with the exception of five and nine species-specific conservative amino acid differences, respectively. The steady-state level of the Tpl-1/Ets-1 RNA and of the Ets-1 protein was modestly elevated in tumors carrying a provirus in the Tpl-1 locus. The relative ratio of the two Ets-1 transcripts, which were shown to arise by differential polyadenylation, was not affected by provirus insertion. Moreover, the major site of transcriptional initiation, which was localized by primer extension 250 bp upstream of the 5' end of the Ets-1 cDNA clone, was shown to be identical in normal cells and tumors carrying a provirus in the Tpl-1 locus. Finally, the differential splicing of Ets-1 exon VII was shown by RNase protection to occur at a rate of 15 to 26% and to remain unaffected by provirus insertion. The subtlety of these effects, in contrast to the strong growth selection of cells with a provirus in the Tpl-1/Ets-1 locus, suggests that provirus insertion may affect the fine regulation of the gene, perhaps during cell cycle progression.

The c-ets-1 proto-oncogenes in Xenopus laevis: expression during oogenesis and embryogenesis

We previously reported the cloning and sequencing of two cDNAs derived from the Xenopus laevis ets-1 gene (Stiegler et al., 1990). The Xl-ets-1a cDNA encodes a polypeptide highly homologous to known ets-1 proteins. The 3'-UTR contains two AATAAA polyadenylation signals together with three copies of the TTTTTAT sequence thought to confer a maturation-specific polyadenylation and implicated in the deadenylation of dormant mRNAs. Several transcripts with maternal characteristics were detected in oogenesis and early embryogenesis. A marked augmentation of the major transcript in the poly(A)+ fraction was detected at fertilization. Ets-1 transcripts were observed at constant levels during the cleavage stages but decreased abruptly at gastrulation, to reappear from neurulation to late embryogenesis. The possible contribution of 3'-UTR sequence elements to this behavior is discussed.

The Ets family of transcription factors

Interest in the Ets proteins has grown enormously over the last decade. The v-ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a cellular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so-called 'ets domain'. The ets domain has been shown to be a DNA-binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein-protein interactions with co-factors that help determine its biological activity. Many of the Ets-related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti-oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets-like proteins may have other functions, such as in DNA replication and a general role in transcription activation. Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T-cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors. G-proteins, kinases and transcription factors. We will discuss how several Ets-related proteins fit into this scheme, and how their activity is regulated both post- and pre-translationally. Loss of normal control is often associated with conversion to an oncoprotein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene-related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets-family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.

The Drosophila gene pointed encodes two ETS-like proteins which are involved in the development of the midline glial cells

Glial-neuronal cell interactions at the ventral midline are necessary for the proper elaboration of commissures in the embryonic CNS of Drosophila. In particular, migrating midline glial cells are required for the separation of segmental commissures. During this process the glial cells recognize specific neuronal cells at the midline, they migrate posteriorly along their cell processes and thereby separate the segmental commissures. The gene pointed (pnt) is required for this glial-neuronal cell interaction, as loss of function mutations lead to a change in the migration behavior of the midline glial cells. As a consequence, anterior and posterior commissures do not become separated and appear fused. Molecular analysis of pointed has revealed two differently spliced types of transcripts, which are encoded in a region extending over 55 kb of genomic sequence. In the CNS both transcript classes are expressed in cells of the midline, including the midline glial cells. Sequence analysis of cDNA clones corresponding to both transcript types reveals two different pointed proteins which share an ETS domain common to a number of transcription factors related to the vertebrate ets oncogene. Furthermore, one pointed protein form contains an additional domain of homology of approx. 80 amino acids in length, which is shared by only a subset of the ETS protein family.

Inversion of a chicken ets-1 proto-oncogene segment in avian leukemia virus E26

The segment of the avian leukemia virus E26 genome near the termination of the p135gag-myb-ets open reading frame contains an inversion of the chicken ets-1 sequence. The inversion contains at least 41 bp and may be as large as 46 bp. This results in the replacement of 13 amino acids of chicken ets-1, with 16 amino acids derived from reverse complement of the normal ets-1 coding strand or read-through into E26 env sequences. At least 13 of these codons are specified by the inverted ets sequences. This represents the first reported occurrence of inverted oncogene sequences in a natural retrovirus. The inverted ets sequences are immediately followed by sequences homologous to the Rous sarcoma virus Prague B env gene. Since the E26 env sequence is more closely related to subgroup B avian retroviruses than to avian retroviruses from subgroups A, C, D, or E, the progenitor of E26 was a virus belonging to avian retrovirus subgroup B.

Characterization of Spi-B, a transcription factor related to the putative oncoprotein Spi-1/PU.1

We have cloned a human cDNA from a new gene, spi-B, on the basis of its homology with the DNA-binding domain of the Spi-1/PU.1 putative oncogene product. spi-B codes for a protein of 262 amino acids presenting 43% overall identity with Spi-1. Its highly basic carboxy-terminal region exhibits 34% sequence identity with the DNA-binding domain of the Ets-1 protein. We showed that the Spi-B protein is able to bind the purine-rich sequence (PU box) recognized by Spi-1/PU.1 and to activate transcription of a reporter plasmid containing PU boxes. Chromosome in situ hybridization allowed us to map spi-B to the 19q13.3-19q13.4 region of the human genome. spi-B, like spi-1, was found to be expressed in various murine and human hematopoietic cell lines except T lymphoid cell lines.

Characterization of Spi-B, a transcription factor related to the putative oncoprotein Spi-1/PU.1

We have cloned a human cDNA from a new gene, spi-B, on the basis of its homology with the DNA-binding domain of the Spi-1/PU.1 putative oncogene product. spi-B codes for a protein of 262 amino acids presenting 43% overall identity with Spi-1. Its highly basic carboxy-terminal region exhibits 34% sequence identity with the DNA-binding domain of the Ets-1 protein. We showed that the Spi-B protein is able to bind the purine-rich sequence (PU box) recognized by Spi-1/PU.1 and to activate transcription of a reporter plasmid containing PU boxes. Chromosome in situ hybridization allowed us to map spi-B to the 19q13.3-19q13.4 region of the human genome. spi-B, like spi-1, was found to be expressed in various murine and human hematopoietic cell lines except T lymphoid cell lines.

Transactivation of erythroid transcription factor GATA-1 by a myb-ets-containing retrovirus

ME26 virus is a recombinant mouse retrovirus construct homologous to the avian E26 virus. Both encode a 135-kDa gag-myb-ets fusion protein which is localized in the nucleus. We have recently shown that ME26 virus can induce erythropoietin (Epo) responsiveness in hematopoietic cells. Mice infected with ME26 virus develop a hyperplasia of Epo-dependent hematopoietic precursor cells from which permanent cell lines can be established. In vitro, ME26 virus specifically induces Epo responsiveness in the interleukin-3-dependent myeloid cell line FDC-P2 by enhancing expression of the Epo receptor (EpoR). In the present study we demonstrate that ME26 virus infection of FDC-P2 cells also results in enhanced expression of beta-globin and the erythroid-specific transcription factor GATA-1, a protein which can transactivate both the EpoR promoter and globin genes. In addition, these cells exhibit a down-regulation of c-myb expression similar to that seen in differentiating erythroid cells. To determine the molecular basis for activation of erythroid genes in ME26 virus-infected cells, we carried out transient expression assays with DNA constructs of either the EpoR promoter of the GATA-1 promoter linked to reporter genes. Our results indicate that while ME26 virus did not directly enhance expression from the EpoR promoter, both it and its avian parent, E26, transactivated the GATA-1 promoter. Furthermore, ME26 virus cooperates with the GATA-1 protein to enhance expression of the EpoR gene. We propose that the mechanism by which ME26 virus induces erythroleukemia involves transactivation of the GATA-1 gene, thus positively regulating the expression of the EpoR and leading to the proliferation of a unique population of Epo-responsive cells. By specifically inducing Epo responsiveness in hematopoietic cells via transactivation of a transcription factor, ME26 virus utilizes a novel mechanism for retrovirus pathogenesis.

Induction of erythropoietin responsiveness in murine hematopoietic cells by the gag-myb-ets-containing ME26 virus

ME26 virus, which was generated by inserting the coding region of the acute avian leukemia-inducing virus E26 into a murine retrovirus vector, encodes a 135-kDa gag-myb-ets fusion protein. Amphotropic murine leukemia virus pseudotypes of ME26 virus induce a high incidence of erythroleukemia 2 to 4 months after injection into newborn NFS/N mice. Spleen cells from the majority of these mice proliferate to high levels in the presence of the erythroid hormone erythropoietin (Epo) and can easily be established as permanent Epo-dependent cell lines. The cell lines contain multiple copies of ME26 viral DNA and express viral message and protein. An Epo receptor mRNA of normal size can be detected in these cells, and binding studies reveal a single class of lower-affinity Epo receptor with an affinity for Epo that is in the range of that previously reported for erythroid cells. The ME26 virus-induced Epo-dependent cell lines, however, appear more immature than previously described erythroid cell lines and more closely resemble early hematopoietic precursor cells, suggesting that the virus may be activating the Epo receptor in hematopoietic cells that do not normally express it. Consistent with this idea, we are able to infect an interleukin-3-dependent myeloid cell line, FDC-P2, with ME26 virus and convert it to Epo dependence. The ME26 virus-infected FDC-P2 cells, even before growth on Epo, showed a large increase in the amount of Epo receptor mRNA. However, no ME26 viral integrations can be detected adjacent to the Epo receptor gene, indicating that the virus is not activating the Epo receptor gene by promoter/enhancer insertion. Our results are more consistent with the hypothesis that the gag-myb-ets-encoded viral fusion protein, which is known to bind DNA, is directly or indirectly activating the expression of the Epo receptor gene in these cells.

Requirement of ets-2 expression for Xenopus oocyte maturation

A molecular clone of the Xenopus laevis ets-2 gene was isolated from an oocyte complementary DNA library. The amount of messenger RNA (mRNA) in each oocyte or embryo was almost constant during oogenesis and was maintained until the blastula stage of embryonic development, indicating that the observed 3.2-kilobase transcript is a maternal message. The only normal adult tissue in which ets-2 mRNA was detected was the ovary. Injection of antisense oligonucleotides homologous to the ets-2 sequence into oocytes led to degradation of the mRNA and blocked hormone-induced germinal vesicle breakdown. The ets-2 product is thus required for the meiotic maturation of Xenopus oocytes.

Sequence-specific DNA binding of the proto-oncoprotein ets-1 defines a transcriptional activator sequence within the long terminal repeat of the Moloney murine sarcoma virus

The ets proto-oncogene family is a group of sequence-related genes whose normal cellular function is unknown. In a study of cellular proteins involved in the transcriptional regulation of murine retroviruses in T lymphocytes, we have discovered that a member of the ets gene family encodes a sequence-specific DNA-binding protein. A mouse ets-1 cDNA clone was obtained by screening a mouse thymus cDNA expression library with a double-stranded oligonucleotide probe representing 20 bp of the Moloney murine sarcoma virus (MSV) long terminal repeat (LTR). The cDNA sequence has an 813-bp open reading frame (ORF) whose predicted amino acid sequence is 97.6% identical to the 272 carboxy-terminal amino acids of the human ets-1 protein. The ORF was expressed in bacteria, and the 30-kD protein product was shown to bind DNA in a sequence-specific manner by mobility-shift assays, Southwestern blot analysis, and methylation interference. A mutant LTR containing four base pair substitutions in the ets-1 binding site was constructed and was shown to have reduced binding in vitro. Transcriptional efficiency of the MSV LTR promoter containing this disrupted ets-1 binding site was compared to the activity of a wild-type promoter in mouse T lymphocytes in culture, and 15- to 20-fold reduction in expression of a reporter gene was observed. We propose that ets-1 functions as a transcriptional activator of mammalian type-C retroviruses and speculate that ets-related genes constitute a new group of eukaryotic DNA-binding proteins.

Definition of an Ets1 protein domain required for nuclear localization in cells and DNA-binding activity in vitro

Ets1 and Ets2 are nuclear phosphoproteins which bind to DNA in vitro and share two domains of strong identity. Deletion analyses of each of these conserved regions in Ets1 demonstrated that integrity of the carboxy-terminal domain, also conserved in the more distantly related elk and erg gene products, is essential for both nuclear targeting and DNA-binding activity in vitro.

Definition of an Ets1 protein domain required for nuclear localization in cells and DNA-binding activity in vitro

Ets1 and Ets2 are nuclear phosphoproteins which bind to DNA in vitro and share two domains of strong identity. Deletion analyses of each of these conserved regions in Ets1 demonstrated that integrity of the carboxy-terminal domain, also conserved in the more distantly related elk and erg gene products, is essential for both nuclear targeting and DNA-binding activity in vitro.

Provirus insertion in Tpl-1, an Ets-1-related oncogene, is associated with tumor progression in Moloney murine leukemia virus-induced rat thymic lymphomas

T-cell lymphomas induced in rats by Moloney murine leukemia virus acquire increasing numbers of proviruses in their genome during tumor progression in vivo and passage of tumor cells in vitro. To determine whether the proviruses progressively acquired during tumor progression play a causal role in this process, we cloned one of them from a cell line derived from the primary tumor 2772. A probe from the cellular DNA flanking the provirus was used to analyze 79 DNA samples from primary tumor tissues of 28 tumor-bearing rats and 80 DNA samples from 30 independent tumor cell lines. This analysis revealed a rearrangement in this region in the primary tumor derived from the thymus of one animal but not in a clone of the same tumor segregating in the spleen. Of the cell line DNA samples, three carried a provirus in this region. Two of these integration events had occurred independently in two clonally related sublines derived from tumor 2772, and they were followed by rapid selection in culture. On the basis of these findings this locus was named Tpl-1 (tumor progression locus 1). The Tpl-1 locus was mapped to rat chromosome 8 and to mouse chromosome 9 at a genetic distance of 1.2 +/- 0.9 centimorgans from the Ets-1 protooncogene. Although the genetic distance between Tpl-1 and Ets-1 indicates that they are different genes, analysis of Tpl-1 cDNA clones revealed that the two are closely related.

Properties of a murine retroviral recombinant of avian acute leukemia virus E26: a murine fibroblast assay for v-ets function

A replication-defective murine retroviral construct, termed pME26, was generated by inserting avian gag-myb-ets sequences derived from the cloned avian acute leukemia virus E26 into an Abelson murine leukemia virus-derived retroviral vector. ME26 virus can be rescued efficiently from transfected NIH 3T3 cells by replicating murine leukemia viruses. Either pME26-transfected nonproducers or ME26 virus-infected NIH 3T3 cells expressed a 135-kilodalton fusion protein (p135) which was detectable by immunoprecipitation with antiserum directed against avian leukemia virus p27gag, myb or ets oncogene protein, or murine leukemia virus p15gag and was principally localized in the nucleus. NIH 3T3 cells infected with ME26 exhibited morphological alterations and increased proliferation in reduced serum and formed small colonies in agar suspension. Discrete foci could be readily recognized in cells maintained in a defined medium containing 0.03 to 0.1% calf serum. In newborn NFS/N mice, ME26 induced a significantly higher mortality and incidence of erythroid and myeloid leukemias. Analysis of a series of mutants affecting the expression of various portions of p135 indicated that the v-ets gene acts to mitogenically stimulate the proliferation of NIH 3T3 fibroblasts and reduces or abolishes their serum dependence. These properties provide an assay system to study functions of the ets gene family.

Mammalian ets-1 and ets-2 genes encode highly conserved proteins

Cellular ets sequences homologous to v-ets of the avian leukemia virus E26 are highly conserved. In mammals the ets sequences are dispersed on two separate chromosomal loci, called ets-1 and ets-2. To determine the structure of these two genes and identify the open reading frames that code for the putative proteins, we have sequenced human ets-1 cDNAs and ets-2 cDNA clones obtained from both human and mouse. The human ETS1 gene is capable of encoding a protein of 441 amino acids. This protein is greater than 95% identical to the chicken c-ets-1 gene product. Thus, the human ETS1 gene is homologous to the chicken c-ets-1 gene, the protooncogene that the E26 virus transduced. Human and mouse ets-2 cDNA clones are closely related and contain open reading frames capable of encoding proteins of 469 and 468 residues, respectively. Direct comparison of these data with previously published findings indicates that ets is a family of genes whose members share distinct domains.

A unique amino-terminal sequence predicted for the chicken proto-ets protein

Avian cellular sequences homologous to the ets domain of the avian leukemia retrovirus, E26, have been characterized, and shown to contain nine discrete regions within a single locus of about 60 kb. The structure of the viral homologous and nonhomologous domains of this chicken ets-1 gene is characterized and seen to define the unique amino acid sequences of the ets protein. We have isolated and sequenced an avian ets-1 cDNA clone obtained from chicken thymus. This cDNA clone contains an open reading frame (ORF) encoding the normal cellular product of 441 amino acids. This product is significantly smaller than that encoded by the v-ets domain of the E26 transforming protein, p135, which contains 491 amino acids. The open reading frame predicted by our sequence data results in a protein calculated to be 50 kDa, which is slightly smaller than that actually observed in chicken cells. The presence of termination codons 5' to this ORF demonstrates that the cDNA characterized contains the entire coding region for the chicken ets gene.

The Drosophila ets-2 gene: molecular structure, chromosomal localization, and developmental expression

The cellular homologs of the ets gene from the avian erythroblastosis retrovirus E26 have been studied in chickens, humans, mice, and cats. In this report a further evolutionary step is taken by isolating and characterizing a Drosophila ets-related genomic clone. Sequence analysis of this clone has shown it to contain the 3' end of the v-ets gene, called ets-2, corresponding to the last two exons of chicken ets. The predicted amino acid sequence was found to have over 90% homology when compared to that of v-ets. This is the highest level of conservation observed for any previously characterized Drosophila oncogene homolog. Expression of the ets-2 gene occurs throughout development, but is highest during the embryonic and pupal stages. By in situ hybridization, the ets-2 chromosomal position was determined to be 58A/B which corresponds to no known phenotypic mutant. As this is a highly conserved gene, the Drosophila model system should prove useful for the determination of the ets gene function.