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Nucleotide sequence of the iucD gene of the pColV-K30 aerobactin operon and topology of its product studied with phoA and lacZ gene fusions.

Gene iucD of the aerobactin operon of the Escherichia coli plasmid ColV-K30 encodes a membrane-bound enzyme synthesizing N6-hydroxylysine, the first product of the aerobactin biosynthesis pathway. The entire nucleotide sequence of the cloned iucD gene was determined, from which the primary and some aspects of the secondary structure of the encoded peptide were deduced. E. coli cells harboring multicopy plasmid pVLN12 (iucD+) hyperproduced an approximately 50-kilodalton peptide which was purified and identified as the product of the gene by examination of its amino-terminal sequence. Two iucD'-'lacZ gene fusions were constructed in vitro and four iucD'-'phoA gene fusions were generated in vivo by mutagenesis of iucD with transposon TnphoA (Tn5 IS50L::phoA). Analysis of the corresponding fusion proteins suggested at least two domains of attachment of the IucD protein to the inner side of the cytoplasmic membrane. The first apparent membrane-bound domain was found within the first 25 amino acids of the protein and showed a sequence which resembled that of the signal peptides.

Amino Acid Sequence↗

Seamless cloning and gene fusion.

Gene fusion technology is a key tool in facilitating gene function studies. Hybrid molecules in which all the components are joined precisely, without the presence of intervening and unwanted extraneous sequences, enable accurate studies of molecules and the characterization of individual components. This article reviews situations in which seamlessly fused genes and proteins are required or desired and describes molecular approaches that are available for generating these hybrid molecules.

Artificial Gene Fusion↗

Analysis of regulation of Klebsiella pneumoniae nitrogen fixation (nif) gene cluster with gene fusions.

Gene fusions in which the lac genes are under the control of each promoter in the Klebsiella pneumoniae, nitrogen fixation (nif) gene cluster have been constructed. These fusions have been used to examine positive control of the cluster and the response of individual genes to repression by ammonia and oxygen. De-repression of nif transcriptional units is coordinate and molybdate is required for maximal expression of the structural gene operon, which is autogenously regulated.

Ammonia↗

In vivo topological analysis of Ste2, a yeast plasma membrane protein, by using beta-lactamase gene fusions.

Gene fusions were constructed between Ste2, the receptor for the Saccharomyces cerevisiae alpha-factor, and beta la, the secreted form of beta-lactamase encoded by the bla gene of pBR322. The Ste2 and beta la components were linked by a processing fragment (P) from the yeast killer preprotoxin containing a C-terminal lysine-arginine site for cleavage by the Golgi-associated Kex2 protease. Ste2 is predicted to have a rhodopsinlike topology, with an external N terminus and seven transmembrane segments. Fusions to three of the four Ste2 domains predicted to be external resulted in beta la secretion from yeast cells. A fusion at a site just preceding the first transmembrane segment was an exception; the product was cell associated, indicating that the first 44 residues of Ste2 are insufficient to direct secretion of beta la; translocation of this domain presumably requires the downstream transmembrane segment. Expression of fusions located in two domains predicted to be cytoplasmic failed to result in beta la secretion. Following insertion of the preprotoxin signal peptide (S) between the Ste2 and P components of these cytoplasmic fusions, secretion of beta la activity occurred, which is consistent with inversion of the orientation of the beta la reporter. Conversely, insertion of S between Ste2 and P in an external fusion sharply reduced beta la secretion. Complementary information about both cytoplasmic and external domains of Ste2 was therefore provided, and most aspects of the predicted topology were confirmed. The steady-state levels of beta la detected were low, presumably because of efficient degradation of the fusions in the secretory pathway; levels, however, were easily detectable. This method should be valuable in the analysis of in vivo topologies of both homologous and foreign plasma membrane proteins expressed in yeast cells.

Amino Acid Sequence↗

Evolutionary origins of the eukaryotic shikimate pathway: gene fusions, horizontal gene transfer, and endosymbiotic replacements.

Currently the shikimate pathway is reported as a metabolic feature of prokaryotes, ascomycete fungi, apicomplexans, and plants. The plant shikimate pathway enzymes have similarities to prokaryote homologues and are largely active in chloroplasts, suggesting ancestry from the plastid progenitor genome. Toxoplasma gondii, which also possesses an alga-derived plastid organelle, encodes a shikimate pathway with similarities to ascomycete genes, including a five-enzyme pentafunctional arom. These data suggests that the shikimate pathway and the pentafunctional arom either had an ancient origin in the eukaryotes or was conveyed by eukaryote-to-eukaryote horizontal gene transfer (HGT). We expand sampling and analyses of the shikimate pathway genes to include the oomycetes, ciliates, diatoms, basidiomycetes, zygomycetes, and the green and red algae. Sequencing of cDNA from Tetrahymena thermophila confirmed the presence of a pentafused arom, as in fungi and T. gondii. Phylogenies and taxon distribution suggest that the arom gene fusion event may be an ancient eukaryotic innovation. Conversely, the Plantae lineage (represented here by both Viridaeplantae and the red algae) acquired different prokaryotic genes for all seven steps of the shikimate pathway. Two of the phylogenies suggest a derivation of the Plantae genes from the cyanobacterial plastid progenitor genome, but if the full Plantae pathway was originally of cyanobacterial origin, then the five other shikimate pathway genes were obtained from a minimum of two other eubacterial genomes. Thus, the phylogenies demonstrate both separate HGTs and shared derived HGTs within the Plantae clade either by primary HGT transfer or secondarily via the plastid progenitor genome. The shared derived characters support the holophyly of the Plantae lineage and a single ancestral primary plastid endosymbiosis. Our analyses also pinpoints a minimum of 50 gene/domain loss events, demonstrating that loss and replacement events have been an important process in eukaryote genome evolution.

Alcohol Oxidoreductases↗

Gene fusion in Helicobacter pylori: making the ends meet.

Fusion genes have been reported as a means of enabling the development of novel or enhanced functions. In this report, we analyzed fusion genes in the genomes of two Helicobacter pylori strains (26695 and J99) and identified 32 fusion genes that are present as neighbours in one strain (components) and are fused in the second (composite), and vice-versa. The mechanism for each case of gene fusion is explored. 28 out of 32 genes identified as fusion products in this analysis were reported as essential genes in the previously documented transposon mutagenesis of H. pylori strain G27. This observation suggests the potential of the products of fusion genes as putative microbial drug targets. These results underscore the utility of bacterial genomic sequence comparisons for understanding gene evolution and for in silico drug target identification in the post-genomic era.

Amino Acid Sequence↗

Finding fusion genes resulting from chromosome rearrangement by analyzing the expressed sequence databases.

Chromosomal rearrangements resulting in gene fusions are frequently involved in carcinogenesis. Here, we describe a semiautomatic procedure for identifying fusion gene transcripts by using publicly available mRNA and EST databases. With this procedure, we have identified 96 transcript sequences that are derived from 60 known fusion genes. Also, 47 or more additional sequences appear to be derived from 20 or more previously unknown putative fusion genes. We have experimentally verified the presence of a previously unknown IRA1/RGS17 fusion in the breast cancer cell line MCF7. The fusion gene encodes the full-length RGS17 protein, a regulator of G protein-coupled signaling, under the control of the IRA1 gene promoter. This study demonstrates that databases of ESTs can be used to discover fusion genes resulting from structural rearrangement of chromosomes.

Cell Line, Tumor↗

Low incidence of mbr bcl-2/JH fusion genes in Hodgkin's disease.

Lymph node biopsies from 140 cases of Hodgkin's disease (HD) and from 30 non-malignant lesions were screened for the presence of t(14;18) translocations involving the major breakpoint region (mbr) of the bcl-2 gene and the joining region (JH) of the immunoglobulin heavy chain gene, using a polymerase chain reaction (PCR) assay with subsequent nucleotide sequencing of amplified bcl-2/JH junctional regions. Expression of the bcl-2 protein within the Hodgkin and Reed-Sternberg (HRS) cells was investigated in 86 cases of HD by immunohistochemistry on cryostat or paraffin sections. Although bcl-2 expression could be found in a proportion of neoplastic cells in up to one-third of HD cases, the frequency of t(14;18) gene fusions detected by PCR was low. We identified such gene fusions in only 3 out of 140 (2 per cent) HD cases, one biopsy of which presented with four clonally distinct bcl-2/JH sequences. No t(14;18) was found in any of 30 reactive lymph node lesions. All fusion gene sequences were unique regarding the localization of the chromosome 14 and 18 breakpoints and the extranucleotide N-insertions. None of these gene fusions conformed to t(14;18) breakpoint sequences previously characterized in our laboratories. Our findings point to a mere coincidence in some cases of HD lesions and cells carrying a t(14;18) in the same biopsy and argue against a significant role of bcl-2 in the pathogenesis of HD.

Base Sequence↗

Use of promoter fusions in Drosophila genetics: characterization of a YP1-ADH fusion gene.

In Drosophila melanogaster the yolk protein (YP) genes are normally expressed only in the fat body and follicular epithelium of adult females--never in males or in larvae. We describe here a first step toward a genetic examination of the developmental controls that restrict the activity of the YP genes to adult female tissues. A YP1 promoter that contains the tissue-, temporal-, and sex-specific controlling elements for expression was fused to the reporter gene, alcohol dehydrogenase (Adh). The gene fusion was transformed into an Adh-deficient genotype. As assayed by a number of criteria, that the fusion gene is expressed in the same physiological manner as the endogenous yolk protein genes. The fusion gene's activity is modulated in trans by a temperature-sensitive allele of the sex determination gene, tra-2. The Adh enzyme serves as a selectable marker and therefore these flies are suitable for use in genetic screens for trans-acting mutations that affect the expression of the yolk protein genes.

Alcohol Dehydrogenase↗

Understanding mesenchymal cancer: the liposarcoma-associated FUS-DDIT3 fusion gene as a model.

Chromosomal translocations entail the generation of gene fusions in mesenchymal tumors. Despite the successful identification of these specific and consistent genetic events, the nature of the intimate association between the gene fusion and the resulting phenotype still remains to be elucidated. Here these studies are reviewed, using FUS-DDIT3 as a model to illustrate how they have contributed to current understanding in unique and unexpected ways. FUS-DDIT3 is a chimeric oncogene generated by the most common chromosomal translocation t(12;16)(q13;p11) associated with liposarcomas. The application of transgenic methods to the study of this sarcoma-associated FUS-DDIT3 gene fusion has provided insights into their functions in vivo, and suggested mechanisms by which lineage selection may be achieved.

Animals↗

Altered Notch signaling resulting from expression of a WAMTP1-MAML2 gene fusion in mucoepidermoid carcinomas and benign Warthin's tumors.

Chromosome translocations in neoplasia commonly result in fusion genes that may encode either novel fusion proteins or normal, but ectopically expressed proteins. Here we report the cloning of a novel fusion gene in a common type of salivary and bronchial gland tumor, mucoepidermoid carcinomas (MEC), as well as in benign Warthin's tumors (WATs). The fusion, which results from a t(11;19)(q21-22;p13) translocation, creates a chimeric gene in which exon 1 of a novel gene of unknown function, designated WAMTP1, is linked to exons 2-5 of the recently identified Mastermind-like Notch coactivator MAML2. In the fusion protein, the N-terminal basic domain of MAML2, which is required for binding to intracellular Notch (Notch ICD), is replaced by an unrelated N-terminal sequence from WAMTP1. Mutation analysis of the N-terminus of WAMTP1-MAML2 identified two regions of importance for nuclear localization (amino acids 11-20) and for colocalization with MAML2 and Notch1 ICD in nuclear granules (amino acids 21-42). Analyses of the Notch target genes HES5 and MASH1 in MEC tumors with and without the WAMTP1-MAML2 fusion revealed upregulation of HES5 and downregulation of MASH1 in fusion positive MECs compared to normal salivary gland tissue and MECs lacking the fusion. These findings suggest that altered Notch signaling plays an important role in the genesis of benign and malignant neoplasms of salivary and bronchial gland origin.

Adenolymphoma↗

Overexpression of translocation-associated fusion genes of FGFRI, MYC, NPMI, and DEK, but absence of the translocations in acute myeloid leukemia. A microarray analysis.

BACKGROUND AND OBJECTIVES: Translocation-associated gene fusions are well recognized in acute myeloid leukemia. Other molecular genetic changes are less well known. The novel cDNA technology has opened the avenue to large-scale gene expression analysis. Our aim was to perform cDNA microarray analysis of acute myeloid leukemia (AML). DESIGN AND METHODS: We performed cDNA microarray analysis using the Clontech hematology filter (containing 406 genes) on 15 patients to study gene expression profiling in AML. As reference, we used whole bone marrow from 5 healthy donors. RESULTS: Our results revealed 50 differentially expressed genes in at least 3 out of 15 patients. Twenty-two genes were upregulated (ratio > or =4), whereas 28 genes were downregulated (ratio < or =0.25). All but one of the 13 genes tested by real-time polymerase chain reaction (PCR) showed the same expression profiles. Among the overexpressed genes, several were those earlier associated with chromosomal translocations and gene fusions. These genes were FGFR1, MYC, NPM1, DEC, and BCL2. The expression of two upregulated genes, HOXA4 and CSF1R, was significantly higher in patients with a white blood cell count higher than 30 x 10(9)/L cells. In patients whose white blood cell count was higher than 100 x 10(9)/L cells, both CLC and GRN were significantly underexpressed, whereas HOXA4 and DAPK1 were overexpressed. FGFR1 and CAMLG were more frequently significantly overexpressed in patients with CD56 immunophenoytpe. INTERPRETATION AND CONCLUSIONS: Clinical and prognostic significance of differential gene expression should be studied with a larger series of patients by using other techniques, such as quantitative real-time PCR.

Acute Disease↗

Detection of fusion genes in sarcomas using paraffin-embedded tissues.

Many sarcomas are characterized by specific recurrent chromosomal translocations resulting in gene fusions. The genes involved in almost all of these translocations have been cloned, greatly changing sarcoma diagnosis. At the biological level, these chromosomal translocations produce highly specific fusion genes that encode key molecules for tumor development. The clinical correlation between these translocation-derived genetic markers and discrete histopathological entities has been remarkable. Today, detection of fusion genes plays a crucial role in the diagnosis of sarcomas that harbor atypical clinical or pathological presentations. The focus of this brief review is the recent impact that cytogenetic and molecular detection of these translocations has had on sarcoma diagnosis using paraffin-embedded sections.

Animals↗

Cytogenetic and molecular genetic analyses of endometrial stromal sarcoma: nonrandom involvement of chromosome arms 6p and 7p and confirmation of JAZF1/JJAZ1 gene fusion in t(7;17).

Endometrial stromal sarcomas (ESS) are rare neoplasms with the capacity both to invade the myometrium locally and to give rise to extrauterine metastases. Cytogenetic abnormalities have been reported in 22 cases of ESS, mostly involving rearrangements of chromosomes 6, 7, and 17. The most characteristic translocation of this tumor type, t(7;17)(p15 approximately p21;q12 approximately q21), was recently shown to generate a JAZF1/JJAZ1 fusion gene. We report three additional cases of ESS with abnormal karyotypes, whose interpretation was based on the combined analysis by conventional cytogenetics and cross-species color banding FISH (RxFISH). The combination of G-banding and RxFISH in every case gave additional information beyond that obtained by either technique alone, determining the identity of even complex inter- as well as intrachromosomal rearrangements. In one of the three tumors, a t(7;17) was seen; molecular genetic studies identified the JAZF1/JJAZ1 fusion gene in this case. Two tumors had aberrations that included structural changes of chromosome arms 6p and 7p. Evidently, karyotypic, and hence pathogenetic, heterogeneity exists for tumors classified as endometrial stromal sarcomas based on their phenotypic features.

Adult↗

Incidence and clinical relevance of TEL/AML1 fusion genes in children with acute lymphoblastic leukemia enrolled in the German and Italian multicenter therapy trials. Associazione Italiana Ematologia Oncologia Pediatrica and the Berlin-Frankfurt-Münster Study Group.

The molecular approach for the analysis of leukemia associated chromosomal translocations has led to the identification of prognostic relevant subgroups. In pediatric acute lymphoblastic leukemia (ALL), the most common translocations, t(9;22) and t(4;11), have been associated with a poorer clinical outcome. Recently the TEL gene at chromosome 12p13 and the AML1 gene at chromosome 21q22 were found to be involved in the translocation t(12;21)(p13;q22). By conventional cytogenetics, however, this chromosomal abnormality is barely detectable and occurs in less than 0.05% of childhood ALL. To investigate the frequency of the molecular equivalent of the t(12;21), the TEL/AML1 gene fusion, we have undertaken a prospective screening in the running German Berlin-Frankfurt-Münster (BFM) and Italian Associazione Italiana Ematologia Oncologia Pediatrica (AIEOP) multicenter ALL therapy trials. We have analyzed 334 unselected cases of pediatric ALL patients consecutively referred over a period of 5 and 9 months, respectively. The overall incidence of the t(12;21) in pediatric ALL is 18.9%. The 63 cases positive for the TEL/AML1 chimeric products ranged in age between 1 and 12 years, and all but one showed CD10 and pre-B immunophenotype. Interestingly, one case displayed a pre-pre-B immunophenotype. Among the B-lineage subgroup, the t(12;21) occurs in 22.0% of the cases. Fifteen of 61 (24.6%) cases coexpressed at least two myeloid antigens (CD13, CD33, or CDw65) in more than 20% of the gated blast cells. DNA index was available for 59 of the 63 TEL/AML1 positive cases; a hyperdiploid DNA content (> or = 1.16) was detected in only four patients, being nonhyperdiploid in the remaining 55. Based on this prospective analysis, we retrospectively evaluated the impact of TEL/AML1 in prognosis by identifying the subset of B-lineage ALL children enrolled in the closed German ALL-BFM-90 and Italian ALL-AIEOP-91 protocols who had sufficient material for analysis. A total of 342 children were investigated for the presence of TEL/AML1 fusion gene and 99 cases (28.9%) were positive. The patients expressing the TEL/AML1 fusion mRNA appeared to have a better event-free survival (EFS) than the patients who lacked this chimeric product. Whereas three of the TEL/AML1 positive cases (3.0%) have relapsed to date, 27 patients without TEL/AML1 rearrangement (11.1%) suffered from relapse. To date, the only subset of B-lineage ALL with a favorable prognosis has been the hyperdiploid group (DNA index > or = 1.16 < 1.6). Our findings reinforce the need to include the molecular screening of the t(12;21) translocation within ongoing prospective ALL trials to prove definitively its prognostic impact.

Adolescent↗

The cDNA sequence and expression of an ubiquitin-tail gene fusion in Neurospora crassa.

The genome of Neurospora crassa contains at least one natural fusion gene encoding a single ubiquitin (UBI) unit with a 78-amino acid C-terminal extension. The predominantly basic tail sequence corresponds to a highly conserved ribosomal protein identified in other organisms. The 0.7-kb UBI fusion transcript is mainly expressed in germinating conidia and other stages of active cell replication. Under starvation conditions attained by nutrient depletion, or after polyamine depletion, the UBI fusion gene is shut off while the polyUBI transcript is preserved. Cycloheximide addition promotes polyUBI, but not UBI fusion transcript accumulation in N. crassa.

Amino Acid Sequence↗

SYT-SSX gene fusion as a determinant of morphology and prognosis in synovial sarcoma.

BACKGROUND: Synovial sarcomas account for up to 10 percent of soft-tissue sarcomas and include two major histologic subtypes, biphasic and monophasic, defined respectively by the presence and absence of glandular epithelial differentiation in a background of spindle tumor cells. A characteristic SYT-SSX fusion gene resulting from the chromosomal translocation t(X;18)(p11;q11) is detectable in almost all synovial sarcomas. The translocation fuses the SYT gene from chromosome 18 to either of two highly homologous genes at Xp11, SSX1 or SSX2. SYT-SSX1 and SYT-SSX2 are thought to tunction as aberrant transcriptional regulators. We attempted to determine the influence of the two alternative forms of the SYT-SSX fusion gene on tumor morphology and clinical outcome in patients with this sarcoma. METHODS: We analyzed SYT-SSX fusion transcripts in 45 synovial sarcomas (33 monophasic and 12 biphasic) by the reverse-transcriptase polymerase chain reaction and compared the results with relevant clinical and pathological data. RESULTS: The SYT-SSX1 and SYT-SSX2 fusion transcripts were detected in 29 (64 percent) and 16 (36 percent) of the tumors, respectively. There was a significant relation (P=0.003) between histologic subtype (monophasic vs. biphasic) and SSX1 or SSX2 involvement in the fusion transcript: all 12 biphasic synovial sarcomas had a SYT-SSX1 fusion transcript, and all 16 tumors that were positive for SYT-SSX2 were monophasic. Kaplan-Meier analysis of 39 patients with localized tumors showed that the 15 patients with SYT-SSX2 had significantly better metastasis-free survival than the 24 patients with SYT-SSX1 (P=0.03 by multivariate analysis; relative risk, 3.0). There were no significant correlations between the type of SYT-SSX transcript and age, sex, tumor location and size, whether there were metastases at diagnosis, or whether patients underwent chemotherapy. Histologic subtype alone was not prognostically important. CONCLUSIONS: The type of SYT-SSX fusion transcript correlates with both the histologic subtype and the clinical behavior of synovial sarcoma. SYT-SSX fusion transcripts are a defining diagnostic marker of synovial sarcomas and may also yield important independent prognostic information.

Adolescent↗